As more and more people create websites, it becomes harder and harder for sites to get to the top of the search engines. When you run a membership website, hitting the top of the search engine can be very important to how well your site will do. There are some ways for you to get there.
[Keep in mind as you read, that not everyone thinks that being in the Top 10 results is necessarily the best thing. There are some studies that show that just being in the Top Forty is good enough, especially as most people will take their time and look around a bit, especially as more people get high-speed Internet and they don't have the same time limits as dial-up connections. As such, being the seventh or eighth site that someone looks at can be in fact a better thing than being one of the first. As usual, your results will vary.]
The key to search engines starts with your website design. When a web designer codes a site, one of the last things coded are the meta-tags that search engines use to decide where a site will go in the search engine's archive. The search engine will index the site based on any other text it can find on the site; the better search engines will highlight the text as it's used when the sites come up. However, there is an additional check going on:
The search engine will compare the meta-tags to the text, and the better the two correlate, the better the site will do in that search engine's results page. This is because, in the early history of the Internet, too many people would put the entire dictionary in their site's meta-tags in order to show up in as many search engines as possible. As such, it was one of the first things dealt with as search engines became more complex.
The other is to have as many links to your site and to have fewer going out. Your best ally here is the discussion board, and the more popular that board, the better. If you can find a discussion board that pertains to your membership site, and post there often, then you will do well in search engines, especially if you have your site in your signature (that little bit of text at the end of postings). If you can become someone of substance on that board, then the more likely search engines indexing that site will be to index your site.
Of course, banner exchanges should be considered as well, especially if the site you are linking from is more successful than your site (remember, you want the linking to be incoming rather than outgoing). If you can find a great exchange program, your site will feel the effects. If you find a way to advertise on a popular site, even if you have to pay for the privilege, then do so the increased traffic will be worth it.
Anything that you can do that brings attention to your membership site will help to increase your standing in search engines. If you can give your membership website positive attention, it will be so much better. You should do whatever you can to spread the word about your site, and do it often!