Speaking of tricks, here is a trick I've been experimenting with recently with much success:
This works very well against certain characters like Marth. If you're at low percent (like if you've just respawned), and your opponent is at death pecents (like 100%+) and you can't find an easy way to kill them, just jump in the air mindlessly like an idiot and don't do anything at all. If you're infront of the Marth for example, he's probably going to jump up and f-air you or something, that's when you double jump through it and n-air the Marth. It's a pretty good trick that I get to work fairly often, it really is a reliable trick to get kills.
You can use the same principal with crouch canceling (Yoshi's double jump is after, very similar to crouch canceling). If you see your opponent (this works really well against Sheiks I've noticed) jump in the air, and you are at low percents, just randomly u-smash underneath them without the intent to actually hit the Sheik in this case. The Sheik will more than likely just f-air you or something in your lag (you make it too good to pass up, you could d-smash/f-smash or whatever, as long as it has lots of lag to bait the Sheik, u-smash is better though imo, because it looks like you were actually trying to hit them and they won't get suspicious...) Make sure you're crouching when you take the hit and just d-smash or whatever after the crouch cancel for a stock.
Yoshi mindgames of the day...