Advertising is your key. First of all start local, get your service onto google maps so that when someone nearby to you breaks there phone and search for a repair by google, your there! and your in London which is even better, with milliuons around you. However this could also pose as a problem as moving up the search engine will take time as there will already be many before you, i was lucky and there were no others in my area (south yorkshire) so i went very quickly to the top.