2 australin lady doctors run a site and podcast called Real Liife Medicine.
They have very good tips on how to get on track, or get back on track etc. I'd start with their blog posts. Very realistic and achievable
Here's their Christmas one, just to get you started
"What should I eat at Christmas?" We get this question all the time. Most people are expecting us to give them a food list or a meal plan, but here’s the thing - there is no one plan that suits everyone. You get to decide what works for you, as what works for you may not work for someone else.