Get a good map
A good road map can save you time and help you discover places and things not in your guidebook
Save some of the headaches and trouble of finding your way by knowing where you're going in the first place.
I am partial to the stupefyingly accurate and storied Ordnance Survey maps, but get whichever works best for you.
A map is more than just how to get from A to B. A good map can clue you into the location of an amazing chalk horse on a hill just around the bend that your guidebook failed to mention (as happened to me on the Salisbury Plain once), or pinpoint the locations of dozens of prehistoric structures beyond the famous one all the tour buses stop at (that one was in Ireland).
A note on road signs (and using them in conjunction with maps)
Also, directional road signs in Europe are funny. Sometimes they do mention route numbers, but not always.
Knowing the route you want is useful, but not nearly so useful as knowing what towns are on that route. This is because road signs at a turnings will point toward towns that lie in each direction.
Here's the tricky part. You never know which towns it will mention. Sometimes it will be just one town, or a group of two to three that all lie in that direction, or sometimes a whole list of a half-dozen.
More confusingly, you never know whether the town(s) listed will be: (a) the next blip of a hamlet the road passes through, (b) the next major town down that road, (c) the provincial capital down the line a ways, (d) the name of the town (could be big, could be tiny) that sits at the next intersection of another major (or maybe minor) road, (e) the regional capital 100 miles down the pike, (f) some other major city 250 miles away, or (g) London.
This is where the map comes in. Take a good look at the next road you need, and memorize the names of all those towns lying along it that might potentially be on the signs (the next dot or two on the map, the first big dot down the road a ways, the really big dot at the end of the road, etc.)