Right, oop norf is a tad vague but here goes.
1) Routing: Using Doncaster as the departure point I'd route to CRANWELL then CAMBRIDGE then EARLS COLNE then SOUTHEND then DOVER VOR then across the Channel to CAP GRIS NEZ. This avoids most of the controlled airspace and allows you to fly most of the flight at 3400' minimum. Cambridge-Earls Colne is a dog leg around Stansted, you may get a transit but I wouldn't be the house on it so plan around. Dover-Cap Gris Nez is the shortest crossing and you can go pretty high over it too.
2) VFR flight plan: File with your tower (if at Doncaster) or your unit, or thru AFPEx if your brave. Personally for your first trip I'd get an Air Traffic Unit to do it. Activate the flight plan when airborne - your Air Traffic Unit will do this automatically, but if its a FISO or A/G unit maybe not - then do it with London FIS. If in doubt as to whether its been activated, ask the tower.
3) Customs. Does the airfield you fly from need a GAR filling out? Check with the club. Doncaster has customs so probably not, but Sandtoft you'll need to notify customs in advance of your ETD and ETA, plus all passport details.
This applies in FRANCE too. Many French airfields don't have Customs on field. Le Touquet used to, but don't now. Check the French AIP plate for Le Touquet at this URL:
French AIP, in the text is an email you have to give 2hrs notice to for Customs. Its dead easy to do, but also dead easy to forget. Every French airfield has different regulations as well it seems - Abbeville seems to be 4hrs notice, Lognes wanted 24hrs last year. French AIP is your source for all that and I can't recommend checking it enough.
4) On-board kit. You need a PLB and lifejackets. If your W&B permits take a liferaft too. Sounds overkill, but so is insurance 99% of the time. Your club should have this stuff or ask around the airfield, so long as you return it I'm sure you'll find someone who can lend you it.
5) Flying the flight. Dead easy really, nothing too complicated about it. I'd speak to Waddington, Cottesmore, Cambridge, Stansted, Southend then Manston who will give you a Basic Service to mid-channel then freecall you to Le Touquet Tower. After that all bets are off - listen carefully, keep a sharp look-out and expect to hear French aircraft calling - AND BEING SPOKEN TO - in French. Someone on here had a good French translation sheet, I can't find it right now but learning phrases such as "vente arriere piste trente-deux" (downwind runway 32 - my French is awful so this could be spelt well wrong!) are useful. Keep your calls clear to Le Touquet, you'll probably be asked to call at Boulogne then join either left-base for 14 or downwind right for 32. Thursday should be a quiet day, so you shouldn't have too much hassle from others joining.
6) Arriving at Le Touquet. On Thursday don't expect to see the follow-me man on his bicycle. Park up at the tower, leave your hi-viz vest in the aeroplane and stroll to the terminal. Pay your €24ish landing fee (steep for France but seeing as how most of their customers are Brits they charge British prices) and then either hire bikes, or get a taxi from outside the terminal. Taxi is €8 each way.
7) In town. Lots to see and do. Get a map in the terminal. The Marche Couvert (Covered Market) will probably be finished by the time you get there, but worth seeing the building. Get an ice cream from Koko on the High Street. We went to La Matisse last time, that was very nice - but so many restaurants you'll find a nice one without any difficulty at all.
8) Going home. Same way you came. The friendly folk in the terminal will file your flight plan and do your fuel (might be worth requesting it when you arrive, they'll do it ready for your return). After you take off Le Touquet Tower will ask you to report leaving the zone and as soon as you report that will say "You may leave my frequency - good bye". This leaves you with a minor dilemma - who to speak to now? Lille probably won't be interested, I tend to tune either London FIS or Manston who say hello and then ask you to report mid-channel. Once back in Blighty its the same route home.
As Alex Orlov says - simples!