Aside from what everyone has already said, I would definetly suggest you do some sort of cardio. I do cardio 4-5 times a week, lift 3 days, and just took up tae-bo.
But yes, even if you are naturally lean, cardio will keep your endurance up, not to mention it will help warm you up prior to lifting. I would suggest getting on the stationary bike for about 10 minutes before you lift. You probably don't need to run, because that would only combat the size you're trying to put on. If you feel you must run, only do about a mile, at MOST.
Also, having a protein shake post-workout will definetely help as well. If you don't have the funds for it (they can be VERY expensive, trust me), then you need to eat some protein after. I'm talking peanut butter, eggs, beef, chicken, whatever. Eat enough, but don't pig out. It's essential you fuel your muscles after you lift to sustain the mass you're putting on.
Overall, I'd suggest just trying different things and seeing what works for you. Since you're new to lifting, and considering your situation, first aim for muscle mass (heavier weights, less reps). But over time, if you see you're not getting the cutness you want, obviously switch up. Plus, go to Barnes and Noble one day, read some of their male fitness magazines (if you can't afford to buy them) if you're serious about this, IMHO.
I've been working out since I was 14 (I'm 20 now). I'm a really aggressive chick, and working out has always helped in releasing stress and keeping me sane -Not to mention the great physical benefits I get
My goal? To look like this when I'm 50!