ahhh yes i used to be a vegetarian...surprisingly people don't realize that what they DO eat has a lot of protein in it even if it's not meat. I'd most concerned with, if i were a vegan, getting enough calcium (which will be fine if you have almond milk or soymilk etc.) and iron, b12 and b6. The b vitamins unfortunately come mostly from animal foods...so usually vegans/vegetarians have to end up taking a B-complex vitamin supplement.
To start off i would ask if you've ever used mypyramid.gov? i find it extremely helpful for figuring out what you're actually getting in the day and it tells you what more you need! you can get an account (this site is USDA based) and you put in your daily food and intake (pretty much liek a food journal). it calculates everything for you, tells you what you've gotten in the day versus what you should be getting so you can see how much you're off by.
I hope this helps! if you have any other specific questions feel free to ask.
p.s. i started a newbie thread!