Wow 140 at 5' 11"? What's your bodyfat percentage?
Change # 1 - EAT MORE! (the most important one!)
Eating more food builds more muscle. Simple as that. What ISN'T simple is the food you eat. GOTTA eat healthy if you don't wanna be about 50 pounds overweight.
First, figure out your lean body mass - take your total bodyweight and multiply by your bodyfat percentage.
Example: you're 140 pounds and 10% bodyfat. 140(.10)=14 pounds of fat. 140-14=126. Your lean body mass is 126.
Second: multiply by 15. Using the above example of 126 LBM, that'd be 126(15) = 1890. This is your maintenance calories - that being, the amount of calories you would need to consume to STAY at your current weight.
Third: Add 500 calories to that. Then 100 calories every week after the first 2 weeks.
Forth: (and this is debatable depending on who you ask) Consume 60% carbs, 30% protein, and 10% fats. No matter what, you MUST consume
at least 1 gram of protein per pound of bodyweight. So if your LBM was 126, you'd consume at least 126 g of protein.
Some bodybuilders recommend going as high as 3 grams of protein per pound of weight... but this can be hard to do. The amount of chicken breasts you'd consume would be horrendous.
Some helpful nutritional information...
Fats are 9 calories per gram.
Carbs are 4 calories per gram.
Proteins are 4 calories per gram.
Good food to eat:
For protein -
Eggs (I believe in eating the WHOLE egg, but some insist on egg whites...)
Chicken breasts
Beef (especially steaks which have high levels of creatine)
Fish (which have EFA's)
For carbs -
Oatmeal (bodybuilders SWEAR by this, and for good reason)
Brown rice
Whole wheat bread
Pasta
Basically, try to stay away from processed junk. Eat healthy wholesome food. You hear this everywhere everyday, but it's good advice.
CHANGE # 2
Join a gym and do heavy compound lifts!
Base your workouts around these compound lifts:
Bench presses
Squats
Deadlifts (careful of these! Done improperly this can fuck up your back REALLY badly - same for squats)
Change # 3
SLEEP! Get
at least 8 hours of QUALITY sleep. Your body produces growth hormones in your sleep, so why cut into your production time? It also is "idle" time when your body can focus on healing itself... making it bigger, better, stronger.
Be careful NOT to over train. 3 days of weight lifting is PLENTY! Don't do more, you'll burn yourself out. Trust me, it happened to me. Took me a year to get back into it (ahhh my idiot days. Wish I knew better then

).
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I reccomend getting
Brawn by Stuart McRobert, especially since you sound like a potential hardgainer.
And don't be mislead by muscle magazines and articles. DO read around (check out this site
http://www.bodybuilding.com/fun/index.html), but cast a wary eye as you read. Some of these programs are designed for AAS users and following these "programs" will overtrain you and you'll never see results (at least not like
they're promising).
Oh! And
DO NOT rely heavily on supplements. Whey protein/Whey isolate protein and dextrose should be all you take. Oh, that and a good multivitamin. And if you wanna get into the steroid game that’s a WHOLE nother world… I personally don’t use steroids, but I understand (and accept) their…. mmmm…. “usefulness”.
Hope this helped. Be happy to help you out more. I
love doing stuff like this. :-D