WTB: is 'Wanted To Buy'
FS: is 'For Sale'

Example Subject Lines:
WTB: MicroATX Socket775 motherboard
FS : Hauppage PVR150 Tuner card/Other stuff

When creating an post in the For Sale/Trade Section, use the above abbreviations to help increase exposure to your ad! It makes browsing for Parts For Sale, or Wanted much more efficient!

How can you sell an item without listing a price?
If you are selling something, list a price! Nothing is more annoying than browsing ads for sale with no clue how much anything costs. Your parts are more likely to sell if you attach a dollar figure to them. Buyers usually skip ads without prices. If you aren't sure what it's worth, do a search for a similar item to see what it sold for or ask around!

Location, Location, Location!
Where are you located?? Listing your location in your profile will also help sales. If someone is browsing for a part and he realizes that you live down the street, a sale is most likely going to happen. If locations are unknown then users are more inclined to skip potential sales in fear of shipping charges or wait time. Edit Your profile HERE and enter your City & State!

For the BEST tips on using our For Sale/Trade forums, please reference this great thread on Anandtech Forums