Hi DAVE.
You will find that there is no such thing as a easy first clean.
You have to remember that wfp is a tool like the squeegy, you need to work from top to bottom, if a window has a top opener you need to do this first and give it time to drip off, if it is over a side opening window make sure you scrub well in the gap between them, thats where most of the crap will be.
Its all about technique and everybody will do it different, but it is mostly about having the confidence to walk away from the job, and this is very hard to do when you first start with wfp.
The ideal way to start is spend a day with someone as trevor says, failing that it comes down to trial and error.
Hope this makes some sort of sense,its very hard to try to explain in words what you do.
Cheers Jeff