Knowing your route and light urban traffic is the single biggest aid to good mpg. Switching off at long lights also makes a big difference. Some you win, and some you lose, but most I win. I believe you have to be switched off for more than 6-7 seconds to benefit.
The wind makes a huge difference. I try to get in behind a big truck, if possible. Not too close (always obey the 2 second rule), but you can see the difference even 2 seconds behind. That is another thing that wet weather effects, as I have to leave a far longer gap.
My wife insists on opening her window, when it is warm, which effects mpg (especially at motorway speeds). Of course I am savvy enough (not brave enough!) to say anything. They reckon that below 50 mph you should open the window and switch off the air con (something I don't have), and above 50 mph do the opposite.