Q. If I do push-ups and pull-ups before bed, will that maximize my gains?
A. NO. A common weight lifting mantra is "the build comes in the recovery." When you lift weights, you create microtears in the muscle fibers, which over a period of days slowly recovery and rebuild slightly stronger (and larger) than before. If you just worked really hard on a chest and back workout, you could actually "shred" the recovering muscles and minimize your gains by even doing a handful of reps later in the day. That's why programs like p90x have rest days and recovery weeks built into them, and why you don't work the same muscle group two days in a row.
Q. I heard Aerobic exercise is the best kind because it burns more fat. Is it true?
A. This statement is partially true, but there is more to the story. Aerobic exercise is any cardiovascular exercise where you are around 70% of your max heartrate. When working aerobically (jogging for example), after you burn through any glucose in your bloodstream, your body uses about 75% fat as fuel and 25% glyocogen (stored carbs in the muscles) as fuel. ANaerobic work, by contrast, is when you are above 80 or 85% of your max heart rate and usually include short bursts of intense work followed by rest (weight lifting, speed work on the track, cardio intervals, circuit training, etc.) Anaerobic work uses 75% glyocogen as it's source and 25% fat. Your body goes for the glycogen in this scenario because it can be utilized faster than breaking down fat, and since your body is in oxygen debt, it will take whatever it can get! However, anaerobic exercise (pretty much any p90x or Insanity workout) is more intense and will burn more calories, and it will also raise your metabolism for longer periods of time after the workout where you will continue to burn calories - and you will build more muscle. The benefits of anaerobic exercise are great, and that is why even if you are a runner, it is important to add at least one speed or interval workout (VO2 max, hill loops, etc.) to your weekly runs.
So the moral of this story is that a VARIETY of exercise is key. If you only do an aerobic run every day, it will not be enough to see major changes.