Most people do, don't beat yourself up over it. The whole concept of discipline and self control seems rather dubious to me.
Some things are easiest to deal with by changing your environment, eat too much junk food then don't keep any in the house, watch too much TV then get rid of the TV, spend too much time on the internet then cancel the broadband connection. I ride my bike everywhere because I don't have a car.
Other things you can trick yourself into doing, if you buy too many sweets when shopping then don't shop when you are hungry and always take a list. If you don't exercise enough then book a regular session with a trainer where the cost of cancelling is high.
Big changes in your life are also a good time to change other things, moving house, getting a new job, getting married are all good times to instigate a new regime.
Be smart about your environment and make the habits you desire so easy to maintain that you won't need self control to stick with them.
2) Incremental changes are incredibly powerful.
Can you manage to study for an hour today? Okay, maybe not - an hour is a long time. Can you do it for 15 minutes? If yes, then do that. And tomorrow aim for 16 minutes. And if you fail, go back to the minimum that you can do and start over. You have 5 junk meals every week - can you have a week with only 4? You probably can and it's a much better way to approach this than trying to eat perfectly clean for a few days and then binging when you have the tiniest slip in your diet.
These small incremental changes work because eventually you hit a point where you're getting a positive feedback loop and what used to be difficult becomes easy. And I think that this is more effective than being your own tyrant - trying to act perfectly and feeling like you failed when you don't meet that expectation.
Your overall willpower is somewhat limited, but the limits of what you can easily do are fuzzy, so you can use that to your advantage by pushing your limits a teeny-tiny bit each day.
