I agree with most of the above:
train as hard as you can, safely.
Eat as much protein as you can, 2gr per kg of body weight is the minimum.
Eat a lot of fiber, protein slows down digestion, fiber helps you absorb it.
Go for complex carbs instead of simple: prefer whole grains to processed. avoid sugar.
Always eat some carbs, before, during and after training. this will avoid your body taking energy from protein, when fat and carbs reserves are exhausted.
You can get everything from food, but its good to have a good suplement (take a shake instead of eating 3 steaks) its more convenient, also if it has some creatin in it, it does wonders, just dont overdo it. I take Nitrotech hardcore, helped me put up 4lb in one month (taking half the recommended dosage).
Dont leave cardio out, its more benefical for muscle tone than what most people think,
also if you want lean muscle, thats the way to go. Do a little before training and a lot after (that way your carbs are depleted, and you burn fat).
Bottom line, if you're going to power train, you need to power-eat.
and, remember steroids make your B@lls shrink