Asymmetry=disgusting and weird. Also, follow Crazyhorse's advice, working out whenever you can is definitely a good strategy. Running is also great exercise, and should not be forgotten.
When doing pushups, pullups, crunches, sit ups, etc. I like to use a mental stimulation as well. Horses way of counting up and down works, but I prefer the '7' method (I just made that name up, so don't try googling it). When you reach a number that contains seven in it (i.e. 7, 17, 27, etc.) you have to do that number seven times before continuing your counting. This means your brain is counting about half of what you are actually doing, and doesn't make you as tired (so, for example, you would count 1,2,3,4,5,6,7,7,7,7,7,7,7,8,9,10,11,12,13,14,15,16,17,17,17,17,17,17,17,18,19,20) So, your body does 32 reps, while your mind only perceives 20 of them.