Hi scwindowcleaning, and welcome to the business.
I used to work for a chartered accountant, so I may be able to help you.
Keep your bookkeeping simple, well organised and up to date. This will save you a fortune at the year end.
(An accountant will be able to sort out a grubby folder of random receipts, but you will pay through the nose for it)
Number each receipt and keep them all together in a folder in order. (wives/girlfriends come in handy here)
You will be able to claim a "fair" proportion of your mobile phone bills (as well as its cost), computer and office equipment as well as software, against tax, but you must be able to justify this if asked by the inland revenue.
(EG if you use you phone ONLY for business, then claim 100%. If half business, 50%)
Motor expenses can be claimed at a flat rate of 40p per mile for the 1st 10,000 miles.
Personally I would ALWAYS recommend using a chartered accountant. The cost will be from £150 - £300 per year plus VAT. If you need to prove your income(to get a mortgage), or sell the business, no-one will even look at you without properly prepared accounts. They'll do your tax return for you too for an extra £50 or so.
Here's a final tip: once you have more than 30 customers, get GEORGE. This is software that will help you to schedule work, forecast income etc. Its really handy. (though the financial reports are feeble)
Hope it all goes well!
The Silly One