ok I'm actually starting this tonight

Wash down walls with sugar soap (I'm using sugar soap solution with a roller as I have rendered brick walls and a spongue will just break up) - sugar soap will get rid of any grime/grease etc
Fix any holes etc with a spacfilla (I don't need to do this - walls not smooth)
Sand over where you've fixed holes
Start painting

You have two choices when it comes to painting
1. cut in the corners/edges first & then paint (with either roller or brush); or
2. paint main parts of wall first and then cut in the corners/edges

I have a paintbrush with a diagonal edge to it for cutting in

Make sure when painting (with brush or roller) that you do not overload the tool as you can get drips.

When picking colours - get pieces of plasterboard and paint the tester colours on there (at least 50cm x 50cm blocks) - sit those against the walls and look at the colours in all lights (daylight and at night under bulbs etc) - that will give you a good indication of the colour in the room (saves painting it on the wall and hating the colour & deciding for something lighter and then having problems painting over the paint swatch)