Tiny tip for demotivated days.... if you are feeling especially unmotivated you could try just doing bodyweight strength exercises. Often doing these is enough to make me feel physically motivated to do cardio, and if it doesn't motivate you to do cardio then at least you will be building your muscles, which also burn fat, so all is not lost!
Diet-wise, one of the best things I ever did was go very low carb and keep my portion sizes appropriate. There's no healthy shortcuts!