in the past few months i've started to run and do push ups/ sit ups daily. its gotten me more in shape than I though it would, not jacked but hey Im doin pretty well.
hang urself off someting so that ur hips are on the edge and lean back with a weight behind ur head or without to start then do a sit up from there, thats al i do for my abs and they is mint.
depends, are you a big kid, or are u a lanky kid, if you just want the toned look do alot of sit ups, if you want the ripped look you have to add weight, do declined crunches with weights on your chest, do alot of oblique shit you know
actually, due to a lack of participation in the weight room last year, our football coach made us do "rewards" (that's what we called em...ironic huh?)
10 pushups
10 situps
10 squat-jumps
10 10yd sprints
and you do em over and over again (at least four or five times through) every day