I think the most important thing is to have the right attitude towards the whole thing. See it as a learning experience (as with everything in life), and don't be afraid to screw up. If it's the first time, you WILL screw up, as everybody with everything. It's not like your life depends on it. No need to panic. Have fun & good luck!
What I know about comp. diet is that it's a rather high protein, and very low fat diet. This seems intuitive b/c the goal is to maintain muscle as good as possible (=lose as little as possible) during the diet, and lose as much fat as possible. It could be that this is NOT the most optimal diet to achieve this, but fact is that most bodybuilders are on such a diet. You should have a slightly negative caloric balance. Also, athletes will increase their cardio work a lot during the diet.
Typically, during a ripping stage, bodybuilders would eat the classic diet of chicken breast + broccoli + rice. Of course you can substitute for the chicken, and eat different grains, fruit + veg. I'd say eating a normal healthy (varied!!!) vegan diet, giving you slightly less calories than you burn (about -250 cal / day will make you lose 1/2 pound a week), maybe supplemented with a high protein meal (protein drink, TVP etc) a day and getting about 10% of your cals from fat would be my choice.
One word about protein drinks and such. I have a feeling that soy protein shakes are overpriced. Soy protein is good, but it should be the cheapest form of protein around. If money's an issue at all for you.
I mean if I'd want to eat a lot of concentrated protein, I'd buy TVP (textured vegetable protein), for about $1.40 / lbs in the bulk section of the HFS. It's basically soy without the fat. 50% is pure soy protein (a complete protein!), the rest is fiber, potassium + a lot of other vitamins and minerals. The tiny amount of 1/4 cup of dry TVP has, IIRC, 11 grams of high quality complete protein!
I suspect that soy protein drinks are TVP ground up + flavoring, sold for like 100x the price. Soy protein is soy protein, and TVP is an excellent and cheap source of it.
Hope to help!
