FIrst thing I would do is just play with the character.
Focus on all aerials. Nair come out really fast, bair cover a wide range, forward air spike and is a good approach, upair kills
After that focus on egg play. Learn to shoot them in the right direction, after that, try to short hop throw eggs. After that, try to shoot egg while moving all the time.
Learn the kills moves (down B, fair upair and smashes)
Learn to mix up your approach with neutral B
Learn to go deep with yoshi, his recovery is good enough that you should pursue most character in the air or spam them with eggs to edgeguard.
After all that, incorporate smash moves and you should be good