just make sure the backdrop behind your subjects is well and evenly lit, that's pretty much it. but its also good if youre shooting people to have a little highlight around their hair with the light, especially if they have a lot of hair.

Any film lighting company in london can rent you lights. AFM, ARRI, LEE, Direct Lighting, VFG.
It entirely depends how big an area you want to light as to what you order. You should also consider what power source is avaiable before you get lights, because anthing over 2.5 kilowatt draws more than a domestic 13amp supply can deliver.
You may also cause an accident unless you are careful with them. If your green/blue screen area is small You may want to hire a basic 3 readhead (800w) kit, but please get them to show you how to use them and dont plug them all in on the same ring..........or BANG!

With that out of the way, when lighting blue/green screen you should consider the image you are trying to match to, or final effect that you are trying to achieve, so that you can blend lighting of the 2 layers.
Light the green/blue screen evenly to a normal exposure.
Have the subject far enough in front of the background so you can light it seperately
Light the subject in the same way that the background image is lit. look at the direction of light. The quality of light, is it hard or soft. The colour etc..
A tiny bit of backlight is nice, but too much and you'll get keys that look like top of the pops 1973.