Try showing him those:
Edgeguarding with Yoshi has some tips that will help, but hold on to the basics and you'll be fine.
1- Don't go for Fair, it's too hard to hit.
2- Go for the Nair. Lard, long lasting hitbox, easy to land.
3- Go for the Dsmash. High range, good angle, spacie killer.
4- Eggs are a nice tool to close angles, usually only one will sufice for an edgeguard, don't overuse.
5- Dash out of stage, Fastfall, Double Jump quickly back onto the stage will get you quickly on the edge.
Recovery it's a whole other story: No tips, you got'ta practice a lot. Learn to read. Learn mindgame.
1- Recovery High.
2- Save your Double Jump.
3- Use eggroll, it'll give you momentum, or change it, it's good.
4- Mixup, Perfect Waveland works, Airdodge works, Nairing works, Groundpound to the ledge works, Raising Uair works.
5- Don't ever commit yourself early, ever. This means no Eggrolling to early, or eggtossing and counting on hitting the oponent to prevent him from stopping you getting to the ledge.
6- Don't get predictable - you have options, and if you don't commit early to any of them specifically it's hard to know where you'll be.