Hi Jessica,
As a general rule expect 1 -2 jobs per 1000 leaflets dropped. Most will come in over the first 6 weeks since dropping, but poeple will keep leaflets for up to 2 yrs or more before they call too. Have your leaflet professionally designed. you can get a local person to do you a leaflet and logo for about £100. Some less, established companies will charge around £250 upwards so ignore them.
Getting your car or van sign written is very good. It advertises for free as you drive about, and also advertises at the house you are cleaning so their neighbours can see you. when you've done your job you can leaflet the 3 houses either side of the client, or even give them a knock too.
Websites are good over the longterm but i wouldn't expect much of an instant payoff. Websites work best alongside leafleting, when you advertise your website on the leaflet. without this not a lot of people will visit your website. i would recommend getting a very simple website to start possibly even a single page one off a designer or done yourself on 1&1 or such like.
May be worth contacting local estate agents about your service. they will typically want the cheapest prices, but when you re new and want experience, and are building up an income it can be worthwhile.
Also call up cleaning companies in your area, offer them a free clean for themselves if they give you work, or something similar, or give them £20 for any client they give you.
For oven cleaning i would not think that canvassing would be very rewarding, but you could give it a try.
Whatever you do get your pricing right. dont underprice yourself. easiest way not to is to get the prices off a franchise such as ovenclean and charge exactly the same.
good luck!