Tell yourself what the reward in the end is if you continue in it :) Also, ask yourself on how important it is, and if it is very important, keep working on it, especially if it's something that you want to do :)

To answer your question I will share my experience: When I have to lose some weight and I have to quit eating sweets I don't buy and bring them home. If I want to stop thinking about somebody, I resolutely delete all the possible contacts of that person from my mobile, friend lists in social networks and try to avoid everyone who could remind me of him for some period of time. Afterwards I make new friends as soon as possible. Talking about the bad habits like smoking or drinking the only way is to start some new really exciting activity immediately and make sure you provided yourself with very tasty snacks for the first hardest period. (Do not think of gaining weight, now you know how to solve the problem later :)

cocaine will keep you going

I alway persuade myself if I keep on it, I wii get success. Every success is not easy to get.

sorry, i meant to put my comment as an answer!