Well, I guess most of the long term veterans of LM will already have a method for sticking the tickets to their windscreen, but for any newbies here is my advice.
The camping tickets come with a peel off section top and bottom, which reveals perhaps the most sticky, long lasting, almost impossible to remove glue which has ever been invented

These tickets need to be stuck in your car windscreen, and often if you have them in your hand on arrival the people on the gate will just peel off the backing and slap them on the inside of your windscreen

My advice is to take a roll of Scotch tape (not sellotape, but it can be anything which peels off easily afterwards) and just prior to arrival make two loops of tape equal to the length of the ticket. Peel off the camping ticket backing and add the two loops of Scotch tape. This can now be stuck to your windscreen and peels off easily and without a mark when you leave.

If anybody else has a tip, please add it.