eat right try to consume as much
protein as possible 300grms to 400 maximum. for legs just do a lot of squats, rev leg extensions, leg presses and try to build the strength i used to force my body to get stronger by upping the weights every two weeks if only by 5-10 pounds for the same reps. My legs are naturally small too i found that just the right amount of sets no matter how bad it hurts and the right exercises work well. for chest i have a draping down chest which is great when its big but its very hard to get big so i do a lot of inclined barbell curls and flat bench adn do a lot of flyes you might benefit from all that too
if you want size try a 5 rep max for each set routine
or do a 4 set 12,10,8,6 reps for each exercise
they both work great
good luck