@Hayley Henning There are many list providers where you can pull leads with NOD or NTS. Most of them are paid services except if you call a title company and ask a rep to send you a list. The downside to this is that you will need to 'process the raw data' as they do not filter parameters for you. A good paid service that I'm currently using is PropertyRadar. Not only can you pull NOD's and NTS's but you can also filter based on equity, transfer date, transfer amount, owner occupied, NOO, etc, etc. I've used a number of other similar services but have found PR to be one of the easiest to use with pretty up to date information at a reasonable price.
As for door knocking, you have to first make sure that you have a good list worth door knocking (e.g. property fits your criteria, it's not pending sale, it's not underwater or has very little equity, etc. - there are ways to make use of this last one but you have to know what you're doing), then have a good idea of what you're gonna say when somebody answers the door, and have ready handwritten copies of letters in case nobody's home so you can stick a letter in their door. From my small experience door knocking, about 80% of the houses were empty.