do it to you own pace and ablity do around 25 situps a day!! if you can do more great the better you get the more you can do this is also a great pilates workout on youtube and they have a mufiin top workout shes great and gives you a great workout http://www.youtube.com/user/blogilates/videos
also theres this exercise where you lay on your back and life your legs up but not to high do that a bit
also chin ups are also a good way.
one tip always pull your stomach in when exerciseing this way you workyour stomach by not doing much. good luck