In this order:
50-50, frontside and backside. Boards front and backside. Lips front and backside. Repeat switch.
Bonus: Move on to front and back tail and nose slides Use a balance shift from board to learn nose slide. If you find the balance naturally, start shifting the other way to dial in your blunt (from your board slide) and nose blunt (from lip). Once you can do them easily by shifting, move to scoring them directly off the ollie. Then learn your 180's off for 50-50's (switch after), 270's off all the slides, then 180 on, 270 on.
1's front, back, cab, switch back. These are the foundation for everything. Learning 3's is hard if you don't know all of these so make sure you can do all of these.
Learn the 6 most basic grabs, indy, mute first, then melon, stalefish, nose and tail. Learn the indy nosebone and tweaked mute before you learn the nose and tail. It will help you score it more easily.
IMO, these are the most basic things you can learn to open up the way to more advanced freestyle riding. But do whatever is most fun, because if you don't, you'll want to quit.