From 15yo to 30yo, I was grossly SKINNY!! no more than 150. The left pic is me when I was 29. That's probably 10% bf, giving me a lean mass of 135lbs. Always ashamed to take off my shirt in public; got teased quite a bit for for being so skinny.
I hit 30 and gained 75lbs in a year. All fat. I hit 235. Today I'm only about 40 lbs lighter, but my body fat is 15%, giving me a lean mass of 165lbs. That's 30 lbs of muscle added and 70 lbs of fat gone.
The last few years has been back & forth with the fat. I'll lose a bunch, still be too unhappy with how skinny I was, then gain it back. I've been working out hard for a few years now. Update 2017: I've been a total slacker this year. Promotion = less time. But I'm back on track now. More fat to lose.
For the first time in my life, not only am I not ashamed of my body, but I'm proud of it. It just about makes me want to cry.
DIET. PLAN PLAN PLAN. Create daily habits. Read and experiment. Try to always eat as clean as possible. For me, taking in a lot of protein was key. If you eat a ton of protein, there's less room for carbs. To lose the fat, just cut carbs / total calories. it really is that simple, just hard.
Lift weights. No matter who you are or what you're trying to accomplish, weight training is your best friend. You will not get too big. I promise. That's laughable because it takes years of very hard work to get even close to big. it won't sneak up on you, no matter what your body type.
Big, compound lifts over isolation, always. squat, lunges, dead lift, bench, dips, pull ups, etc. The most important things are hit in the first 1 or 2 exercises each day. That's where the magic happens.
When you do an exercise like squats, you're taxing your cns a lot. They are exhausting because they hit so many muscles and in a big way. The cns responds by becoming tougher, and releasing hormones and stimulating processes which make you stronger. Plus, the more muscle you have, the more your body produces what's needed to build muscle. And squats put pounds of muscle on faster than any other exercise. Again, it's still a very slow process. I've learned that from reading hundreds of articles and then watching how my own results improved a great deal after I started to get serious about the big compound lifts (squats, dead lifts, good mornings, dips, bench, standing press, rows, shrugs).