When I first became an agent, I learned how to develop my sphere of influence through networking, sending post cards and pop by's. I had an agent training me in the Buffini System. Just some things that I learned on my own.
1. Call clients at times that are convenient for them. If they work at night, don't call them while they are sleeping.
2. Don't just show up. Call ahead of time and arrange a meeting so that it is convenient for the client.
3. Be real. Don't be a fake and don't sound like you are reading from a script. Many people just read the script. Clients know when a person are using one. Remember telemarketers.
4. Keep in contact at least monthly. Most people liked the agent they bought a house from, but very few can remember their agent's name. These people are a great basis for referrals in the future. Especially if they had an excellent experience with you as their realtor.
5. Finally, just use common sense. That will be your best asset.