Fly as often as you can, minimum once a week. Otherwise you'll spend a lot of time re-learning stuff.
Prepare for each lesson and memorize the procedures that are going to be trained.
Use a flight simulator to train the procedures that can be trained in a FS, e.g. VOR radial interception and tracking, getting lost and figuring out where you are through 2 VORs, NDB / ADF stuff (don't know if this is PPL stuff in the UK).
I did this and saved a lot of time and frustration. Didn't have to repeat a single lesson.