I can give you some tips from someone in the same boat as you. 6'1" and 150lbs forever nomatter what.
When i started my
lifting routine i took the high calorie, high protien GNC shakes and did them by the book! I also would eat eat eat, didn't matter if it was healthy or pizza and burger, i just would eat it! Healthy is good, but some fat won't hurt you if your matabolism is like a hamster as mine is.
Anyhow, did the high calorie shakes for 3 months to supplement my
calorie intake and protien. Also creatine and eventually N20.
Im pleased to say that since Aug 1 ive put on a solid 10lbs of musle and my strength is a LOT better. I went from a max bench of 140lb, to 230lbs in 5 and a half months with hard work.
I am off the high cal shakes and just drink protien before and after my workouts along with my creatine and N20.
Ive put on enough mass that everyone can tell, and my shirts fit a lot diffy. By the 12 month mark (aug) i think i will be pleased with my first year in.
Good luck, check your progress every 4 or 5 months with lifts. As you get bigger your gonna get stronger too

Get some protein too and stick to it the best you can.