Many people go for the hammock style setup, with tarps and liners and all that, but I never got on with them myself. Stick to small, low tents or make a bivvy.
Think about what you'll do in the evenings, as it's surprisingly easy to get very bored, very quickly. Perhaps take a friend?
Get out to Scotland if you can, as it's somewhat more legal there.
Otherwise, get your OS map out and pick small areas of woodland around farming fields, far away from any paved routes and ideally a little way off footpaths. You want to avoid random dog walkers happening on your camp. Also keep an eye on the ground as you get to site, and scout the immediate area, looking for any sign of human existence, especially food wrappers and alcoholic drinks containers that suggest it could be a popular place for young/mischevious people to visit. You definitely don't want them intruding on you!
Think about your method of fire/heat and choose something that doesn't put out a lot of light or smoke. You should have a lightweight folding shovel anyway, so consider digging a pit for your stove, or putting some kind of shroud around it. Similarly, get a torch with a low-lumen 'moonlight' mode and get used to working with that.
Get a couple of books on Escape & Evasion, especially the military manuals. You'll find plenty of useful tips on staying hidden in those... just skip the parts about covering yourself in mud and lashing your Rambo knife to a stick, while digging spike pits. You don't want to be that guy!!
