1) Google 'General Aviation Report Form'. Fill it out, then fax it to both the police force governing the airfield you're taking off from and the one you're landing at.
2) File a flight plan, do it at least 24 hrs before you fly to be safe. If you need any assistance see if you can visit the peeps in the tower at Blackpool, most ATCs are happy to help, usually they can file it for you.
3) Lifejackets, and know how to use 'em.
4) Assume the weather is going to be ok in the days leading up to the trip. On the morning, check weather along route and 100 nm in each direction to get an idea of the general picture.
At the end of the day, all you're doing is the physical act of taking off, flying a certain distance, and landing again. Don't let the paperwork put you off! Over the sea for the first time, you'll be constantly worrying about the prop stopping/failures etc... Try not to overworry, just enjoy the flight !
For the first trip, I'd recommend a GPS as an aid to your other navigation techniques. Anything to reduce your workload is good in this situation.
Have done this journey many times and from many different angles of the UK, no issues thus far!
Oh yeah, don't forget to close your flight plan. If the airfield you're landing at is ATC, ask them if they can close it for you after landing/turning off the runway/changing to ground freq etc. Otherwise there is a phone number somewhere, Google will have it no doubt.
Enjoy
p.s. Should probably add, this is just my way of doing it. Not necessarily the right way!