You may have heard a theory that it takes 90 days, or 10,000 hours to change a habit. While there is some truth in that, there is another level to changing habits, and that is 'deep practice'.
In a health and fitness context, deep practice can be applied to various objectives; from losing body fat, to improving fitness or refining sports skills. The repetition involved in deep practice begins a process known as 'myelination', which can be seen as the coating to an electrical wire, and allows the electrical signal which is sent when the brain 'fires' during an activity and allows it to move quickly, lending itself to a higher degree of accuracy in behaviour.
As we begin to repeat something, it allows us to refine a skill. So where does the development of a new habit come in? In fact, rather than directly coming from repetition, we can credit it to something which very few people like to do - making mistakes. Expose yourself to making a mistake - because it gives you the opportunity to learn something. It allows you to analyse and refine your behaviour.
Take changing your diet. You are likely to make some bad food choices along the path to a healthier diet. But instead of making you give up entirely, those mistakes can lead you to analyse where you went wrong. Did you plan your lunch break badly? Perhaps you have given in to the temptation of your favourite fast food chain after a hard day at work? Making the mistakes will allow you to take stock of what happened, and plan to change your behaviour the next time you are in the same situation.
Start to embrace repetition, the struggle that goes with it, and the mistakes you will inevitably make, with the determination that you will stay on track. And finally, embrace replication - find role models who are doing what you want to do, or behaving in a way you want to behave; there is no shame at all in trying to replicate their activities.