Bert take a look at the current offers of window cleaners software ... George, WCP (no longer upated), aworka (my fav), cleaner planner - Sorry if I have missed any.
Give them all a spin and see what suits...hey you may just prefer pen and paper or perhaps a simple spreadsheet.... Horses for courses but don't over complicate the whole thing...... the complicated part is what the accountants are paid for i.e knowing the in's and outs of the tax system, loopholes, area's where you can and cannot push the rules....
If you are already VAT registered or will be soon then I suspect you'll want professional advice anyhow but our end it is not that complicated.
But do remember the taxman will pretty much know what most professions in any given region earns, spends, house type, etc, etc.... infact most professions and people will be in certain 'brackets' of the population..... stick your head out of those brackets too far and then you're looking to get an internal cavity search from HMRC.
Have a search through this forum for a plethora of back-posts, threads about software, just like strippers we'll all have our favourites just like window cleaning software

Cheers & Good Luck