Right at your weight, try to get at least 175-200 grams of protein.
For this you will probably need to use a protein or weight gain supplement to help get the extra protein grams. I have used a few weight gainers, they are mostly all the same.
some good ones:
Progain by maximuscle
N large by prolab
Take 1 or 2 drinks a day along with 3-4 meals and try to start eating more lean chicken, beef and other meats....just eat a shit load of food!
In theory, gaining weight is simple.
Lift wieghts, eat like a cunt and rest = weight gain
good luck