1) Keep a record of your diet for 5-7 days. This will give you an idea of what your caloric intake is. A lot of people are surprised to learn they aren't eating as much as they thought, or are eating more than they thought if trying to lose weight. Use a site like fitday.com for help.
2) Foods: whole grains, good fats, lean proteins. When I'm bulking my main three meals look like this:
Breakfast: 4 over-easy eggs, 2 slices of ezekiel bread, 4 slices of turkey bacon, 1/4 steel cut oats, 16oz. 2% milk.
Lunch: Big ol' turkey sandwich with some sliced block cheese and turkey pepperoni, some pretzels for a side, banana or mandarin oranges, 8 oz. 2% milk, 1 can of tuna in water.
Dinner: 10-12oz. of steak (rare), 1/2 cup broccoli, 1/2 cup whole grain rice. I'll eat other meals between the big ones but those are the main meals of my day.
3) Cut back your cardio. That means parking closer to your destination, take the elevator, increase your rest time between sets if you do weight training.
Those are the key things I implemented and went from 170lbs. of skinny with a 150lb. max bench to 185-ish lbs. of moderate muscle with a 290lb. max bench in about a year.
Thanks for this! Lots of great info!