I've found treating myself helps. For example finding a new healthy recipe that I haven't tried before or buying myself new exercise clothes. Sounds a little silly but they all make me look forward to testing them out later on in the week so it pushes me to carry on each day. I found it tough for the first few weeks so decided to gradually decrease and/ or change food items one at a time. If you've been snacking or eating unhealthy for a long time then a dramatic change can be too much for your mind to cope with, thats were I realised I kept failing. I don't do slimming world, just calorie count at the moment, but like Ali said any plan will work as long as you're eating the correct amount of cals a day
Online / group support will really help keep you on track too. Hope thats helped and good luck with it all