what EASTO said.
Make sure your forms good, lift heavy, eat alot, get enough rest, and don't leave out major movements like DEADLIFTS, Squatts, bench. U wanna gain, start doing deads. Just work on your form gradually add more. I gained ALOT of weight and strength once I encorperated deads into my workout.
I've had alot of luck w/a program called the power matrix lift 8, 5, 3, 1,1,1, 5
For example...if someone can bench(can be used for squatts, deads 2) 350lbs max, their program would look like this- 215x8 260x5 280x3 320x1 320x1 320x1 260x5
If u wanna try it out let me know what weight u're at MAX and i'll give u the #'s ya need. Just remember having proper form and lifting less is more important then lifting more and sacrificing form.
also heard alot of good things about the 5x5
Sometimes, plateaus can be caused from something lacking in your diet.