I'm 6' and 145 too! Actually I'm 5'11'', but yeah, I'm really skinny. I lift weights and sometimes I do go up to about 150, but then I go back down, and I also swim so I burn too many calories. What I would suggest is compound exercises like squats, deadlifts, bench press, pull ups and push ups. Also you have to eat a lot. Probably around 3000 calories a day, if not more. But spread them out so you eat about 5-6 meals a day. My lifestyle is currently preventing me from eating that often. Fruits and vegetables are important, and you have to eat them, but also eat foods that have a lot of calories like pasta, potatoes, etc, cause chewing on lettuce all day long won't give you 3000 calories. That doesn't mean eat junk food. I'm not a big fan of milk cause I think it's unhealthy, but there's this website that says if you drink a gallon of milk every day and do squats 3 times a week, you're guaranteed to gain weight. If you drink that much milk you'll probably gain a little fat too though. Good luck!