All through high school I never weighed over 135, and at 5"11 was pretty damn skinny.
Now I weigh a hell of a lot more and am still lean.
Here's my suggestions in a nutshell.
Eat, pick a number of calories and eat that much every meal, 5 times a day. If you don't gain weight up the number. I suggest starting at 500 calories, but you may have to go to 700 or higher (doubtful, but you never know). The healthier the food, the less fat you'll gain. Brown rice, oatmeal, etc. Some fat in ever meal except post workout. Post workout drink a quart of non-fat milk and whatever fibrous carb source you want (fruit, granola bars, bagels). Drink 3.0 liters of water (or more) daily. 30-40 grams of protein each meal. For more food stuff look at John Berardi's articles.
Cut the smoking out, I never smoked so I can't really comment on what it feels like, but it's nasty.
Train 3-4 days a week, screw your abs for now. Keep your workouts short 8-12 hard work sets. Chin-ups, dips, bench press, rows, squats (if you can rig something up, I used to use dining room chairs when I had no gym access), lunges, shoulder press, barbell curls. Keep the reps fairly low and the weights heavy ideally, you may need a few weeks of lighter weights to get your form down and to avoid massive soreness, avoid going to failure.
Train each exercise once a week, if you make progress then you are doing fine. Maybe 2 or 3 exercises a workout. Example squats and lunges. Done. Bench Press and rows done. Dips, chins done. Curls and shoulder press done. As soon as you make excuses on your diet, you will come to a crashing halt.