pure instinct... nothing i do is going to change how i look, so i don't think too hard about it.
to give you an idea of what i might do for leg day:
4-5 x ~10 sldl
4-5 x ~10 squats
1-2 x ~20 leg press
5 x 10 calf press (using leg press)
increase weight each set, or maybe do the last 2-3 sets at the same weight
some days i do 5 x 5
or maybe 3 rep sets for just a bunch of sets
sometimes just one exercise but 10 x 10
it doesn't matter... it's all the same in the end.
i do 2 leg days, one "pressing" day, and one "pulling" day each week. on friday i try to do 50 snatches in a reasonable amount of time.
i run for 20-30 mins 3 times a week at a moderate pace (if i'm on the treadmill, start at 8 mph end up at 9.5, adding .5 mph each 5 mins).