I’m exactly 110lbs and around 5’8", so I know how you feel. Rolling with 210lbs guys all the time is annoying, but I have no problem beating them consistently. Yes, it can be done. My biggest advantage over them is more mat time. Spend more time on the mat. If you train once a week, go twice a week. If you don’t want to do this, then try to scrounge up new submissions from the internet to surprise your opponents with.
Some people suggested bulking up. Let’s say you gain 65lbs of pure muscle and now you’re 200lbs. Then you’re gonna be posting here asking how you can beat the 300lbs guys (hey, just like that other guy in this thread). There will ALWAYS be somebody bigger and stronger than you, is the point. Plus, bulking up takes much more time and effort than spending a few extra hours per week on the mat.
Now, if you don’t want to do either of these things, then your opponents will be both larger and more experienced, so you’ll basically be fucked.
I’ll start you off with the three techniques that I always use for beating a larger opponent. This is going to be a massive post, and I mean absolutely gargantuan, but I’ll try to organize it as best I can. Learn how to:
Take somebody’s back.
I like doing this when people try a single-leg takedown on me. I keep my leg between their legs - that’s one hook 
- and then I just kinda circle around and get my other hook in there while securing an over-under grip (one arm across their neck, one arm under their arm). This may require above average flexibility, and yes you won’t be able to get the leg they grabbed properly hooked. This is a really unorthodox move, but hey, you’ll need to be as crafty as possible if you want to beat much larger opponents.
I also like getting back mount from guard. This is an art. BJ Penn did it to Matt Hughes in their last fight, just so you can witness what I’m talking about. Your goal here is to get one of your opponent’s arms on the other side of your head that their arm is usually on. This part usually isn’t that hard if you maintain tricep control. Then, their back is unprotected. Let’s assume you manage to get their left arm to the left side of your head (your left). Get your first hook in by opening your guard up and sticking your left leg between your opponent’s thighs. Scoot your hips out towards your opponent’s left side (their left). Get your right arm over their back and grab their right lat (grab below their armpit). Hoist yourself up there and get your right hook in. This part is very difficult, especially when done fast enough.
The standing arm-drag will also lead you to a glorious back mount victory. This is my personal favorite way to get back mount. This is used to get behind your opponent, either by pulling them towards you or by pulling yourself towards them (which ends up happening with us smaller guys). This is not an easy technique by any means. Once you’re behind them, you have three basic options. You can take them down from behind, or you can hop up on there, get your hooks in, and take them down from there (there is a way to do this that involves pushing one of your legs into their thigh while pulling their upper body in the opposite direction and leaning towards that side a lot.) OR you can hop up, get your hooks in, and choke them, if you’re a crazy bastard. The way with the highest rate of success is to take them down from behind. There are a few ways to do this. Here’s my favorite. 1) Encircle their hips with your arms, which you should ALWAYS do the moment you get behind somebody while they’re standing, unless you plan on taking their back while they’re standing. 2) Lift your knees and legs straight up - yes you will fall down. Place your feet against the backs of your opponent’s knees right before you hit the floor and then push. Timing is everything here. 3) Easily get your hooks, and start choking.
Also learn how to:
Triangle choke. Learn how to spot openings. Learn how to make openings. Learn how to secure it so that your opponent can’t break free. Learn how to finish it and tap your opponent out.
Spotting and making openings is too complex to explain here, let alone on the mat. Just experiment and see what works. But I will say that popping your guard open, lifting your hips up, and clamping your legs on your opponent (one on their neck, one below their arm, in case you couldn’t guess) is a ridiculously fun way of slapping on a triangle while your opponent is trying to break your closed guard open by forcing their elbows into your thighs. Speed is crucial here.
Keeping the triangle choke. This is one of the few things that I’m not going to label as “difficult”. I’ve given up maybe one triangle choke, ever. It’s a ridiculously tight submission with almost no hope of escape for your opponent, if you do it properly. Here are some pointers.
If your right leg is draped over their neck, hook their left leg (their left) with your right arm IMMEDIATELY so that they don’t lift you off the ground. Switch the sides around if your left leg is draped over their neck (duh). Don’t bother with this if it’s unfeasible for your opponent to lift you off the ground.
Tighten your triangle choke as soon as possible.
Some people get one leg around their opponent’s neck, and one leg under their opponent’s arm, and then they cross their ankles. This is a “loose triangle”. You must minimize the time your legs are in this position. Zero seconds is the goal. Also, no leg-over-top-of-foot stuff (like in the kempofist vs andy fight). Get your ENTIRE foot past the crook of your knee, then flex your foot upwards to make sure it can’t slip out. The crook of your knee should be resting as high up on your other shin as you can manage, but getting it resting past the top of your other foot is absolutely crucial. Going from a “loose triangle” or a leg-over-top-of-foot situation to a fully locked up triangle can be hard, especially if your opponent’s shoulders are broad, so here’s how to deal with that.
If your right leg is over your opponent’s neck, pull your right shin with your left hand and bring it towards you so that your left leg can rest where it needs to be. Fast, easy, and effective. If your opponent is so large that even this is difficult, then here’s what you should do: angle yourself off from your opponent perpendicularly. What I mean by that is if your right leg is draped across their neck, scoot your hips so that your right leg is in line with the rest of your body and your body is perpendicular to your opponent’s body. You can make this process easier for yourself if you hook their leg with your arm and use this to pull your body in that direction (if your right leg is across their neck, hook their left leg with your right arm). Angling yourself off like this will allow you to sink the choke in more deeply. If your opponent isn’t a huge beast, you can probably tighten the choke just fine without angling yourself off, but angling yourself off will always lead to a tighter choke, in my opinion.
Keep control of their trapped arm and make sure it stays across your chest/across their neck. Don’t let that arm escape. Otherwise your opponent may hook their trapped arm under the thigh of your leg that isn’t across their neck, completely preventing you from finishing the choke from that position. (You can counter this with an omoplata, or fight to get their arm back, but the point here is that the triangle is a fantastic move for all fighters, especially the smaller ones, so you shouldn’t give it up if you like winning.)
Pull down on their head, HARD, with both hands if possible. This will prevent them from moving around as much and it is also done when applying the choke in an attempt to tap your opponent, once you’ve finished locking it up.
Finish the triangle choke.
Not every submission will work every time on every person. This is like some kind of golden BJJ rule. Bah. In my opinion, there are enough ways to finish the triangle choke so that even the most stubborn of opponents will be greying out. One way is to just pull down on their head as hard as you can while squeezing your knees together. If this isn’t enough, you can try looping your arms around your knees, clasping your hands together, and using your arms to force your knees together. Note: this method of finishing is most effective if you haven’t angled yourself off from your opponent. My personal favorite way of finishing the triangle choke is to hook their leg with your arm (if your right leg is across their neck, hook their left leg with your right arm) but instead of doing this to angle yourself off perpendicularly, you’re going to fold your opponent. Bring their left leg to their head. Your left arm can either grab their head or grab your right heel, or whatever. This will pretty much crush the shit out of them.
I’ve heard that the less of their shoulder (of their trapped arm) that you can see, the better. I don’t really pay attention to this, but it might be useful to you.
Also learn how to:
Ahilles lock. Sadly, although this move is great for larger opponents, as somebody pointed out earlier, the number one easiest position to do this from is in your opponent’s open guard, which basically never happens if you’re a much smaller guy. This leaves you with achilles locking from the bottom, which is always scary as hell. My advice: learn how to do it while your opponent is standing. This way, they aren’t on top of you, and you also don’t have to get them on their back. If this means you have to resort to the hated butt-scooching strategy, flying scissor takedowns, and other generally crazy shit that results in ankle locking a standing opponent, then so be it. Standing, kneeling, whatever. As long as they aren’t on top of you. http://youtube.com/watch?v=8ldw-TFeZqY&mode=related&search= Use this guy as inspiration. Don’t be afraid to try the move that he does at 29s; I’ve used it to set up an achilles lock before.
Also feel free to go for the achilles lock during a scramble, like during the ensuing scramble after doing the backdoor escape from mount. That’s the one where you get your feet in your opponent’s armpits and then you roll backwards on your shoulder.
Also, learn how to set up the achilles lock from within your opponent’s guard/open guard, on the off-chance that you somehow get your larger opponent on his back.
Actually applying the hold is not something I have any good tips on. Just think of it as a guillotine…on their achilles tendon. Bony forearms help. Feel free to crank the hell out of it, it’s a safe submission. Plus, your opponent might tap because OMG LEGLOCK. I’ve won more with the achilles lock than with any other move at this point, even though I’ve only been going for it recently. It’s a hell of a move.
I hope you survived that. Enjoy.