The most important part of metal detecting is the bit you do before you go out....RESEARCH !
What i always do is research the area I am going to search prior to getting anywhere near it. This is useful for pre-planned trips like when I went to Belgium last year. I got hold of 2 or 3 'in depth' books on the Ardennes offensive (1944-5) and then read them from cover to cover, noting down any interesting references. For example, one book had a quote from an American soldier saying '...it took us 3 days to clear the Germans out of the woods between 'village x and village y'......' So, up pops google earth, I find the villages, identify the woods, go and search....FINDS !!!
Same goes for England. Don't just go to an area because it used to be an airfield......research what happened to it. My brother went MDing for the first time at Steeple Morden, an old USAAF base. I warned him that there were NO remains of runways or any buildings and that he probably would have trouble finding stuff. But he went any ways. He found 347 million bits of aluminium foil and we later found that the farmer used recycled landfill 'compost' to put on his field.......which was full of mashed up aluminium foil !!! This was on a website so he could have saved himself 4 hours of time.
Find somewhere with identifiable buildings or old ranges where you can get the precise location or even old POW camps as many of these were out in the country. Then research them and use google earth to identify how you are going to get to the site and where you're going to search.
The old saying should always be foremost in your mind.....for every 20 detections you get 19 bits of crap and 1 good find......live by that and you'll enjoy it more
If you get lucky with a site like me, the saying gets reversed by the way