New here and Need Help!

I own and operate two sites for fun. If possible I may be able to get a business' to place ad's on my site. Like I said these sites are for fun not profit. I want to get more members though. How do I get my sites to pull in more members with search engines. Are there any tricks you could show an average person to make their site more visible. I have been able to figure out quite a bit from hands on experience as far as operating the sites goes. I thought it might be more than I could handle but sar far so good. Thanks ahead of time for any help you may be able to give.
Thanks again

There are no "tricks" per se. First, the site has to be something of interest. (although going by some of the things I've heard of being sold on Ebay I guess just about anything could be :) ). It needs exposure. And it needs to keep interest.
One key area to focus on is search engines. This includes making things easier for the search bots (sitemap, valid nav links, proper mark-up, etc.), and changing/adding content to keep them coming back.
And another area is "word of mouth". Having content that others will want to link to increases your exposure and helps your SERPs.
And you could consider user participation (blog comments, a forum, image uploading etc.) too.