Buying a used car from a dealership

I'm on the look out for a new car. I've identified the model, age and spec I want but they are not around in huge numbers, so my choice is a little restricted. It seems I'll have to buy through a dealership, which I've not done in a very long time, and even then it was a cheap runabout. There seem to be a few on the market at around £9-10k, but I'd like to knock £1k off that. Is a realistic aim? If so, how best to haggle / negotiate? I did read that the second half of June would be a good time to do this, as they'll be approaching the end of a sales quarter and keen to hit targets. How can I avoid getting screwed over by the Swiss Tonys and Arthur Daleys of this world? All BBS advice welcome, ta.