MarketingVox has a great article on how to increase Googlebot’s crawl visits and site indexability. The Googlebot visits some sites more often than others. Often indexed sites are thought to be more appealing to Google and on searches, they’re likely to appear higher for relevant keywords.

Here are a handful of tips that may encourage search spiders to visit your site more often. Most are old SEO standbys:

1. Make sure you’ve got a sitemap, which enables spiders to locate new pages more quickly. (Once spiders are on your site, they have a limited time to crawl content before moving on. Guiding them through your site can help them dig deeper.)

2. Keep your link and semantic structure simple. Duplicate content should also be kept at a minimum; sifting through it wastes precious time that could be spent indexing unique material.

3. Update content daily. And if not daily, then consistently — a few times a week would be good. Relevant sites keep their material up-to-date, and often updated sites — such as news sites — are sometimes crawled several times per day.

4. Try to win link love from other highly-relevant, generously-updated sites in your field. Think of quality links as votes for your site’s importance. (Avoid link farms, though; Google cracks down on fishy-looking linkback practices.)

5. Minimize page load time. Remember a spider’s time on your site is limited; don’t force it to crawl through the hinterlands of gigantic images and heavy PDFs.

6. Is your content hidden behind a form? Here’s news: spiders can’t see past them. Tactical SEO consultant Bruce Clay recommends cloaking forms for spiders. (This is considered by some experts to be a black-hat tactic, potentially punishable by Google, so tread lightly. Clay says major liquor brands, which are obligated to ask at outset whether a site visitor is over the legal drinking age, cloak forms for spiders as a matter of course.)

7. Bear in mind other obstacles that may delay indexability:

• JavaScript Links — they are totally invisible to search engines. Avoid using them to manage site nav, as links in JavaScript code are likely to be ignored.
• Links with query strings are thought to be avoided by spiders. Database-driven sites build on ASP, PHP, Cold Fusion or JSP often sport query strings in their links. For more on this, check out the “Query Strings” section in this Key Relevance article.
• DHTML drop-down menus — goes back to the JavaScript issue. While these are popular means of guiding people from A to B, spiders have trouble interpreting the JavaScript code used to create these menus.
• Flash has long been an enemy of spiders, but Adobe is working with Google and Yahoo to make Flash indexable. That’s well and good, but a Flash-heavy site still affects pageload time. Feel free to be pretty, but keep laggage low.
• Frames — these make it possible to blend content from multiple pages onto a single page, based on the instructions of a “master” or “frameset” page. Most of the time, spiders can crawl the homepage — which typically houses the frameset tags — but it won’t be able to see the other frame tags composing the rest of your site. If your site has frames, make practical use of the “noframes” tag. Here’s more on that.