OK then ... ready for this ... (information is from NCMA Members Handbook, 2005/2006) ... if you work 40+ hours/week:
Heating and lighting - One third of your bill (33%)
Water rates - One tenth of your bill (10%)
Council tax - One tenth of your bill (10%)
Wear and tear - One tenth of your total earnings (10%)
If you rent your property - One tenth of the total rent (10%)
Reasonable costs of cleaning household items can be allowed as a separate item
Food and drink - whatever you specifically buy. If you make batches of food and use half for your family, only claim half as an expense.
Telephone - any business-related calls on landline or mobile. If half your calls are business, then you can claim half your line rental (if 10%, then 10% of line rental etc.)
Any presents for children (so long as you wouldn't normally buy for that child).
Trips/outings - entrance, food etc. both for mindees and yourself.
NCMA membership, public liability insurance, cost of any courses, toys, equipment, stationery, toiletries (loo rolls, wipes, nappies etc) and so on. There's obviously lots of other sundries!
Hope that's enough information! If it's of any consolation, I tend to do my tax return just days before it's due in. I'm just a lazy cow, basically!