Taking one day at a time
There are some days which you feel energetic and then there are some where you feel you are slogging and demotivated. That's our first lesson right there. Just do the right this for today. Its okay. You will feel better tomorrow.
Don't get tempted
There are just too many things so commonly available that will get you tempted. Just remember processed foods like sugar are the demon worth fighting against. If its getting too difficult to control, remove yourself from the position
Celebrate often but with the right rewards
An alcoholic, trying to leave alcohol, doesn't celebrate 1 month win by drinking. No! what they do is acknowledge and celebrate in non-alcoholic way. Similarly, when you loose weight, you shouldn't have a food party. Instead reward yourself in non-food related manner. For example buy your self that gadget you really wanted from long time, or take some time off and relax at the beach!.