Start by thinking about what you know you can do. Maybe it's 10 sit-ups, maybe it's 30. So go out there and do three more than you thought you could do. Hold a wall sit for 30 seconds instead of 20. Run hills instead of running around the track. What's hard for you on Monday will be easy for you on Friday... if you push yourself everyday, that is. Just keep in mind, if it's not hard for you then it's not doing anything for your body. You should be challenging yourself everyday if you want to see improvement!
As for diet tips, try to not eat after dinner. I know this may seem crazy and nearly impossible but if you make sure you're always full before leaving the table, it'll be easier than you think. If you eat before bed, that food just sits in your stomach and you're not burning off those calories like you are throughout the day.
You'll feel so much better going to bed at night knowing you worked hard and you're getting closer to that goal. It may come more easily to someone else but that's just another reason for you to work a little harder and push yourself a little farther.
So get out there and do it because I know you all can!
