From personal experience, I know that it is much easier to get people to visit your site the first time than it is to get them to come back. In this article, you'll learn some good ways to get people to return to your site regularly.
I look at things from a "noncommercial" site point of view here. By that, I do not mean only sites that offer content without advertisements or Web shops, but sites that do not have retail and product sales as their primary objective. This could be a site that offers news, product discussion and reviews, and places for users to interact with each other, but that is still aiming for a small profitor at least to be able to finance its site by sales and advertisements.
Content in General
The biggest factor in all this is, of course, the general content of your site. Remember to keep the topic of your Web site well defined and focused, and try to specialize in one area instead of having one huge site that really can't support all the topics it deals with. I have learned that building up a "frequent visitor" base works only if you have in-depth content on your site that is unique and highly relevant to a certain topic. This is vital if you expect users to become members or to visit your site frequently.
The overall number of returning users will be greater if you discuss a couple of well-covered topics on the site than if you cover a lot of topics in a very superficial way.
Try to expand your site only after you have developed a big enough member (or frequent visitor) base to be able to support additional areas on your siteboth in financial and physical terms. Don't make the mistake of expanding your site without expanding your manpower if you can only barely handle the current number of topics handled on your Web site.