There are a variety of steps to take when promoting websites.
I'll list them, its up to you to look them up and figure out how to accomplish each step.
On page SEO (search engine optimization)
-This includes a strong inter-linking structure, relevant content, etc
Off-site SEO (also known as link building)
-Includes getting links from other RELEVANT sites, containing the appropriate anchor text (In your case you would want to use "Auction(s)" "Car Auctions" "Boat Auctions" or whatever your general niche is.
Directory submission
-Submitting you site to a list of relevant web directories
Other advertising avenues-
Such as: Google Adwords, Yahoo Search Marketing, Microsoft Adcenter
This should give you a good start to boosting the amount of traffic and interested parties visiting your site.