Google Spider Frequency

• Get a High PR page. Google will visit often.
• If you want Google to spider more often update content regularly -once a day if possible, or at least every other day.
• Use a revisit meta tag on your pages - <meta name="revisit" content="14 days">
• Try external linking from PR5, 6.. Pages to your deep pages (second and third level pages)
• Static Site map linked from home page
• Get plenty of inbound links ideally to the front page and a few inside categories or sitemaps, since google might not index that deep on new domains.

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Reference:
http://forums.seochat.com