Yo man, I'm kinda at the same stage as you. Started working out end of summer and got possative results but then went on a bit of a lads holiday and fucked off the exersize after.

I was slim and toned in school and had a high metabolism to and I've started putting some good weight on. I mean I'm not massive yet but I'm medium and toned at the moment and I'm not expert but I will tell you what I do.

(got these tips off my dad who used to be manager of a sport center, is a personal trainer and a circuit training instructor)

I do 3 sets of each workout with reps of

12
8
6

Each time, but with only 10 seconds rest in between each set. This is to be done with reasonably heavy weights, I couldn't give you a weight to do because I don't know what your capable of, but basically you just want to be able to just about finish the last 2 reps of each set if you get me. Start with a weight that gives you a bit of resistance then after a month it should get easyer then up your weights.

So its 12 reps, (rest for 10 seconds) 8 reps (rest for 10 seconds) 6 reps. Stop change exersize.

I aslo use creatine monohydrate as a suplement and eat a massive omelette after every work out. Creatine seems to be giving me reasonably decent muscle defenition compared to my work outs with out it, but only been using it 2 or 3 weeks. And creatine is totally natural. But its just something I'm trying, my dad would recomend protein shake.

Hope this helps.