do you have experience cleaning? think how much you want to pay, e.g. £7 per hour (you can find out average if you look at local job centre cleaning jobs) and then add holiday pay to per hour, e.g. 0.75p per hour needed for holiday, plus N.I, plus then take a rough guess at how much cleaning equipment will cost you, then add that up, say at the moment every 1 hour cleaning you'll lose £9.50 at minimum. then add whatever you want to make profit from it and that's your price per hour.
what i find is much harder to work out is how lnog it takes to clean, so 3 bed house could be 5 hours for me, but only 3 for you, so even if your pricing £15 per hour and i'm just charging £11 per hour, i'll still be much more expensive.
best way imo to get foot in the door is start google adwords advertising as it's immediate results and you can quickly back out if you decide it isn't working for you, though you will need a website.
hope this helped
good luck