How can I get better and better at acting besides acting classes and joining local plays?

Eh, you need someone to play off of. Acting isn't something you "practice" like doing scales on a piano. The best way to get better is through experience and taking on challenging roles. The bst way to do this is through plays and classes, exactly what you're doing. The benefit of classes is that you have the opportunity to tackly roles you might not necessarily get in a real situation. (eg. taking on someone who's older or younger, someone more of an ingenue if you're not, etc). Natural talent is the big key here, however I think great acting comes down to honestly, believability, connections and being present. Some people are naturally better at these things and some never really "get it". But find a good class with teachers who will push and challenge you and you should be able to discover things you wouldn't necessarily learn in a rehearsal situation. Doing plays is where you get to apply your knowledge and technique. If there's things you want to do on your own, I suggest reading plays. Read as many as you can and begin making a list of "dream" roles. Also, look for monologues in them - ideally you should have a stockpile at your disposal for use at any time - comic contemporary, dramatic comtemporary, comic classical and dramatic classical are the basic categories. The way you determine if you're actually good at acting is if you get cast on a regular basis. When you're first starting out, you'll get the small roles, but your goal should be to work up to the leads.