Hello, I'm a fairly new Melee player (been actively trying to improve for a couple months) and I've gotten down some basic tech skill like wavedashing, L cancels and SHFFLing. My question is, where do I go from here? What skills should I develop right off the bat while I continue to improve my basic tech skill, and what can I do to improve? I'm still having trouble deciding on a main as well.
Pretty much its already been said by those above me.
The bit I would like to add is to try setting some goals for yourself and it should help you on whatever you decided to do. If you aim low your results will generally be limited. If you only want to beat those around you, then you will probably end up doing things that only achieve that and nothing else. However, if you aim high it can help you focus.
With that in mind you might find yourself with a bit of a trade off that is not to your liking. Captain Falcon might be cool to get tech chase reads with in dittos, but you would find greater success sticking with probably less entertaining methods like Uthrow -> regrab on his tech chases instead since its guaranteed if you do it right. Or if you want to go to nationals and make like top 8 you should probably stick with a good character like Marth, Sheik, Jiggs, Peach, Fox, or Falco.
Again, set your goals and let that drive you. Otherwise, the advice you get could be what you need or not need depending upon your goal.