Advertising is a form of inbound marketing. You put a message out in some way and wait/hope/pray someone will call you. All can have some success but it can take a long time and you have no control. I much prefer, and have been more successful with outbound marketing. One way is what the previous poster mentioned. Get out and talk to people whom you can help and they can help you.
The other key is to (1.) decide on your target market e.g. pre-foreclosures with equity, pre-foreclosures with no equity (short sales,) probate, owners with very high equity (over 75%), private note holders, out of town owners, owners of multiple properties, etc. etc. (2.) Establish an outbound marketing program - phone calls or door knocking. Go to them, don't sit and wait for them to someday decide to contact you. While a letter would be good for an introduction (such as probate, out of town owners , and private note holders) I follow-up with a phone call no more than four days later, or visit if local. Face time is key to fast success.