How do you guys typically get in on opponents? My j3 gets AAed more often than it connects, I feel his biggest flaw is starting momentum
Getting in is the hard part with Joker in alot of MUs because his mobility is crappy. You have to keep your opponent guessing, and it's different in every matchup. No offense at all, but I have heard from GGA commentators that you're a bit predictable with the j3's, which is probably why you're struggling. I am alot of the time as well, and people that play me often tend to blow me up for it. Just have to adapt your playstyle to be more patient, something I'm working on as well.
Sometime you can rely on dash cancel mind games with the gun and tossing around teeth from a distance for meter and as a threat. This isn't always an option though. Good zoners like Zod, Deathstroke, and Sinestro force you to block and dash your way in for the most part. You can mix in guns at times to keep them honest, but you really need to know the frame data alot of the time and it can be risky.
Something I like to do is get within sweep/jump distance and just throw far teeth at them. It's punishable if they make the read, but not really on reaction. If they try to catch you, push block them into the teeth. What most people will do, though, is play cautious and try to jump. Then you've got them; catch them with a j3 if they jump back and go into the d2 xx mb RLG combo, or if they jump at you, you should be able to get them with a d2 on reaction into a combo ending in crowbar for OTG setups.
And don't forget that going in isn't always the best option. Sometimes you just wanna sit back and zone with gunshots and teeth. Again, it all depends on the matchup. What gives you trouble specifically?