Try a protein shake with 3 raw eggs, milk, and fresh strawberries (for flavor) every day in addition to your normal everyday diet. That should be a start and it worked for me. As a standard disclaimer, I don't claim to be a dietician, nutritionist, or anything related.
I only ask this because I am scrawny! I could put a lighter touch to the comment and say, I'm a little bit skinny, or I'm pretty slim, but I'm only cheating myself. It also winds me up when people say "Count yourself lucky, I would love to be like you." Yeah, great. If I could hand over the reigns of my bone clinging physique, I would in a flash.
I spent a period of time just chowing everything in a fit to get stocky, I ate fry ups, pasta, jacket potatoes, but it just didn't seem to work. My cousin once mentioned that he's the same and he managed to put on weight once by drinking those body building drinks, but I don't know if that's a good idea just to put on weight!
Somewhere, something incredible is waiting to be known.