Posted: 03/05/2012 at 14:01
I've been doing this for 6 yrs now so in addition to Wintersongs good advice I'd add:
Have an overall plan in your head of how you're going to use the different areas of the garden (seating, veg, play areas, shed, greenhouse etc) and refine it as you see the impact of taking out stuff you don't like or which is getting past it's best. That way when you start working on a section you'll be thinking about how it will link into other sections you are leaving til later.
Don't rush it - as you work around the garden you'll start to know it's little foibles of soil, sun, water etc which will help you put the right plant in the right place first time
Mark out potential paths etc with string, bricks, hosepipe - anything temporary and start using them before you cut them. That way you can see if they feel awkward and adjust them before it's too late
Good luck and have fun