I try to remember to do 8-10 vertical push ups (hands on the ground, feet high on the door frame so that my body's almost straight up and down) whenever I enter or leave my room.

I try to do this at least every other day:

(3x) 8-12 pullups, sprint up a steep hill 3-4 times, 20-30 push ups, 8-12 chin ups
Jump rope (normal, alternating feet, and one-footed). I've never timed myself doing this.
Some kind of ab exercise

On the days that I don't do that, I ride my bike.

Sometimes I'll run a few miles .

I want to build muscle/mass in my arms, but I don't want to lose my six-pack. Suggestions?