How much should I exercise and what are the proper ways to exercise? I exercise like almost every 3 or 4 days a week, each time is different work-out. I did my abs work- out today and it cause me neck pain. How can I do sit-up without forcing my neck?
You could do leg-lifts instead of sit-ups. Lay flat on your back with your legs straight and then as slow and steady as you can, lift them up without bending them until they are straight up in the air then lower them back down slowly. Repeat as needed. It does the same ab work without putting stress on your neck/back.
Personally, for flute playing, I find that the yoga pose 'chair pose' or the martial stance 'horse stance' (they are very similar) are really great for exercising those muscles and diaphragm control. I've gotten to where I often stand in horse stance or tree pose when practicing because it makes my tone much better and keeps me a lot more aware of diaphragm.