first i would like to direct you to this
fitness forum
but i will try to answer your question to the best of my knowledge.
First, the very basic formula of gaining weight is calories that you intake > calories used.
Thus, i would suggest you on eating 2500 to 3500 calroies a day if you are planning on gaing some serious weight.
Second, ther rule of thumb is you want to eat 1 gram of protein per lb that you weight every day.
So for example, if you are 150lbs, you need to eat atleast 150 grams of protein a day.
A good supplement is whey protein shakes, which you can pick up at your local GNC store.
I recommend a brand called Optinum whey, its cheap and fairly good whey protein
3rd, you need to set up a workout regiment.
Such as monday for chest, tuesday for legs, wednseday rest, thurday shoulders/back, fri rest, sat arms etc.
Try to avoid working out a same muscle group without 48hrs of rest in between the workouts.
It will not help your muscle development but rather stunning it.
That's all i know as of now and anyone else please feel free to provide more information
