First thing Ill say is we all do it!!! So dont beat yourself up.
I usually get myself back on track by setting myself a mini goal. Like a hair cut or nails or something. If you think of something you really want or need then I get excited and eager to work towards that.
If my food is letting my down a bit sometimes ill sit and work out what i want to eat for a week and trial different things and put it on the fridge.
As for the smoking I gave up 6 months ago and i was nawty and had a few on nye but didnt make me wanna start again. I stopped cold turket when the no smoking in clubs came about, but its different for everyone. I used to find something else to do when i thought i needed a smoke like paint my nails or file them or something.
Hope i was a little help!