It's real simple.
Diet. Diet. Diet.
You get that right and the workout matters very little...as long as you lift heavy.
Don't worry you will never get big like a bodybuilder...unless you are doing the things that they are doing which includes more then muscle milk.
1 gram of protein a day per lean pound of body mass.
1 gallon of water everyday at a minimum.
ONLY two shakes a day. (I prefer one for breakfast and one post workout. I like to include dextrose in my post workout but thats a personal preference.)
Chicken Breast, Fish, Chicken, Fish, Turkey, Chicken Breast.
Eat a hypo-caloric food at night such as green beans or cabbage.
Throw in red potatoes or sweet potatoes...
You will see some results.
But if I only weighed a buck fifty...I would eat my butt off and hit the gym like a mad man. You probably have a high metabolism and just need to stoke the fire with good calories.
(I have been working out 15 years and have seen literally thousands of 150 lb guys wanting to get cut or get big on the latest gimmick. Two things that I have found that work...Creatine and protein. The other thing is called "hard d#$% work")