I've been using a phone app called "Way of life"
It basically asks you to set goals and then everyday it will prompt you asking you to provide answers for the day.
So if your goal is not to gamble - put gambling in, it will ask "Is gambling good for you?" - click NO, and then every time you enter that you didn't gamble for the day you get a green block for that day. It will remind you if you forget to enter it.
Here is where it gets interesting...
I created 2 topics, one called "gambling" (yes/no) and one called "feeling good" (yes/no)
Over time as I was trying to quit, sometimes I would gamble and feel good (if I won), usually I would gamble and not feel good and so on... The main thing is that you are honest with yourself, otherwise this won't work.
Over time, as I scroll back - there's becomes a very very obvious visual link between happiness and gambling. Happiness never seems to last when gambling is happening, but it always comes back after a while when gambling stops.
I found this app to be a really useful tool - it also chains together successful days and reminds you how long you've been going for. Sometimes when we look back, it's just a blur of misery and losses, if you want to remember when you succeeded and failed, and how it made you feel.. this is a good way to do it :-)
A whole week of green blocks is a massive boost to self esteem