Fresh Content is the best way to get a spider to visit your site. This is a really, really important subject to post so we will do so in another post. You can’t dictate to a spider how frequently it visits your site or what pages it visits. Search Engines know how frequently your pages get changed because they store some of the information they retrieve every time they visit. A sitemap will help, having good navigation architecture in your site is a must and it’s good to link to new pages, especially critical ones from your index page as that’s the page spiders will visit more frequently. The best thing to do is create fresh content. The more engines visit and find new content the more frequently they will come back.