If you're like me (skinny caused by fast metabolism) then you need to eat more often as a first thing. Like have a proper breakfast ( i know u coffie/cig junkies ; ) and then be sure to eat something (doesnt need to be a lot) every 2-3 hours. For me this works a BIT (i.e. slooww growth, but growth), in order to really gain weight I need to train 3x a week and eat gainer (carbohydrates) and then I grow.