Knocking... brings in the most, but is very time consuming.
Leaflets... 0.5-1% hit rate.
Website... a real must for every business in my opinion. You need to get people to look at your site - printed on van, leaflets, advertise in free local places, advertise on google
Emails / phoning companys - you have to get the data TPS checked or you could get into trouble. Also unless your experienced on the phone it can be hard to speak to the right person.