Hi Stu
I started my own window cleaning business back in February,all the info and advice is here,you will need some time to read through all the posts but well worth it.
Buy some basic kit, like I did, 14'' applicator, (Unger Monsoon),a squeegie with 10'' and 14'' blade,couple of scrim cloths,get a sample of window cleaning solution, I use GG4 , there is plenty of information on all types of cleaning fluids on this forum, all my original kit I bought from Wintecs, speak to Mark very helpfull.
There is also a lot of info on insurance here.Ladders I got from Lansford Access in Bristol , excellent ladders.
Practice and practice on neighbours and friends houses.Prepare a flyer, post them through doors and go back a couple of nights later and knock there door and introduce yourself, people like to see who you are, I have found this has worked for me.
Remember you are learning all the time and be professional.
Any other details you need just send me a PM
Best of luck
Steve