good sir, the only thing that will advance your yoshi game (besides the unluck spotdodges : ( ) is egg tosses and pivot grabs. also, bair is a great approach (yoshi's best), but it became predictable.
short egg tosses followed up by grabs (or anything really) are a good. ETS (egg toss slide) helps with getting the right spacing for eggs. egg tosses are invaluable, because those things are f'ing frustrating, and projectiles always make people approach you differently (and generally in brawl, you want people approaching you). even if they dodge your egg toss, go immediately after them (if close enough) with something, dash attack/fsmash/jab/running usmash is what i use. if they don't dodge it, run in and grab, then "do yo thang". egg tosses are clutch for me.
pivot grabs (more grabs in general). people HATE yoshi's tongue. be careful to not get into the habit of grabbing too much, yoshi can get punished on his grab lag. grabs really help you control the flow of the match, especially the cg's (check the yoshi guide sticky).
you have a great yoshi, just learn ETS (egg tosses in general, they're great damage and they start combos for me) and grabs. and watch out for mario's bair, nair, and fsmash!