The best guide to visiting English sites I've come across - by far - is James Dyer's "Discovering Prehistoric England" (ISBN 0-7478-0507-5). Unfortunately, I've not found anything remotely comparable covering Wales, Scotland or Ireland.

I'd therefore recommend browsing online resources such as TMA, Coflein and Canmore and getting to know what's in a particular area before you go.... don't try and cram too much in at once... and avoid honeypot sites at peak times. In my opinion, quality visits really count over quantity.