This is one of the best kept secrets of many successful domainers. The following will get you list of potential buyers.
- Find the owners of domains similar to your name from whois record. ( http://whois.sc ) . So for eg: if you own Cards.com check who owns cards.net, cards.org etc or ecards.com, icards.com, cards123.com and so on.
These are the companies who probably first search for cards.com and since it was already gone they got alternate names. Since you own "better" domain, chances are they would want that. The key is that your domain should be better than the buyer you are contacting.
- Find Advertisers who advertise on such names. For eg: if you own DomainSellingtips.com there are 3 keywords here, Domain, Selling and Tips. Check who would advertise on these keywords. Your first option is to goto Google.com and search for Sponsored links on these keywords.
- Next goto Overture.com and search for keywords in your domain name. Click "View Advertiser's Max bids" to get the list of all advertisers.
Once you have generated a list of potential buyers from above technique, contact them individually ( NOT MASS EMAIL as it may be considered as SPAM ). Then follow TIP 5: Contacting Private parties and corporates.
Remember you are into Sales you should be willing to accept NOs, No replies, criticism, its all part of game. Make sure your techniques are ethical and legal. If you are asking $10000 for a domain, you can recieve a counter offer of $10, there is no need to feel bad or offended, it just means that you did not explain the value of your domain to buyer.
Once you have contacted all the buyers from above list and have not recieved any response, move on to next domain.