Best way to improve my diet to see results in muscle gain?

Not sure if that is exactly what I mean. I do not want to become 350lb monster or something so that is not what I mean by gaining muscle.

Though I would like to reach around 200lbs or so. I currently weigh about 150–160lbs which is average for my height.

I have cut out soda and other useless drinks for this past year now(plan to keep it that way) take a multivitamin everyday, attempting to eat more healthier foods. Specially more greens.Overall cut out ALL the junk and be more balanced is my main goal.

But also to become more bigger without being huge, yet gain muscle and definition would be nice.

Any ideas as to get to my goal(s)?