I've been going to the gym for years, but only seriously been going since March 09, so thats 16months. I'm naturally a slim build, but by religiously lifting weights 3 or 4 (depending on program) times a weeks i've grown quite considerably. However, due to this i've now got some quite ugly stretch marks around the arm pit area of both arms due to the growth, so be weary of that.
At first I was doing just weights and football, but a good few months back I started running at the end of each session (2-3miles) and boxing on rest days, as well as cycling to and from work instead of driving. The hardest part now is fitting it all in, but I've managed to get it so my typical week is:
Obviously with cycling thrown in between that where I can. Due to the increase in CV I won't gain weight as quick, though because i'm working different body parts each day i'm still progressing, and following months of sticking to this weekly routine I feel great.
If you just want to get big - just go for weights, though if (like me) you want to still gain size and be very fit in general then consider doing something similar as me.
Saying that, if you need size to start with as I did then you would probably be best just doing weights for now mate.
Go to the gym with a specific programme targetting different areas of your body, aim to take in around a gram of protein per kg of your body weight and to eat natural foods, stay away from fizzy drinks and alcohol!
Infact, I put together a new programme for myself yesterday which will do me for 4-6 weeks (always change it up after this point).
Day 1 (chest and triceps)
Bench Press 4x6
Bench Press (I) 4x6
DB Fly 4x8
Bench Press (D) 4x6
Skull Crushers 4x8
Day 2 (back and biceps)
Lateral Pull Down 4x8
EZ Narrow Curl 3x8
Seated Row 4x8
Hammer Curl/Twist 3x8
Reverse Fly 4x8
Day 3 (shoulders)
Upright Row 3x8
Pull Ups 3x10
Shoulder Press 3x8
Barbell Curl 3x10
Front Raise/Lat Raise Superset - 3x10
Cardio/Abs routine to be followed after each workout
I'm avoiding leg weights at this moment in time do to my legs being over worked as they are, and as i'm training for something which involves a fair bit of running I can't risk another leg injury or else i'm in big trouble, otherwise I would of done legs on the same day as my shoulders (squats, extensions, leg press, calf raises etc). Due to the fact I cycle a fair bit though, which is quite heavy on your quads i'm still getting the release of testosterone which comes from working them, which of course helps you grow, so i'm not sacrificing too much by not working them with weights at the moment.
If you want, print out my workout and work to it, like I said though, change it up after 4-6 weeks.
Any questions mate then PM me, I should be able to help you out. If you want to know how to perform any of the exercises then again just ask. If you're going to do it, aim for a ratio of 4:2 (four second release, followed by a two second lift), I've found that's the most effective way to gain size, and aim for total muscle failure after each set, with a rest no longer than 60 seconds in between. Have fun!