Take the practice exam on Salesforce University's 501 certification site.
And most important is to have patience. The 501 exam is a much slower process than 201 or 401. Although it's improved since I've taken it, it took about 9 months from start to finish for me, and I was able to get into the first programming assignment window.
http://www.salesforce.com/us/developer/docs/apexcode/salesforce_apex_language_reference.pdf
http://www.salesforce.com/us/developer/docs/pages/salesforce_pages_developers_guide.pdf
http://www.salesforce.com/us/developer/docs/daas/salesforce_migration_guide.pdf
thanks,
http://www.forcexplore.com/2014/06/salesforce-dev-401-dumps.html
By not typing in all upper caps / "yelling". Kidding aside, the links posted by sfdc_wave are a great start. I'll also add a few items:
Order of execution is important. https://www.salesforce.com/us/developer/docs/apexcode/Content/apex_triggers_order_of_execution.htm
You'll want to study the various controllers you can use with visualforce, and how the order of those effects class loading, for instance.
Object oriented features like private / public / global and what those mean.
Read up on these other blogs here:
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http://www.forceprepare.com/advancedeveloperfaq.html
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http://www.sales4s.net/salesforce-advanced-developer-certification-501-study-notes
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http://corycowgill.blogspot.com/2011/05/passing-forcecom-advanced-developer-501.html
Take the practice exam on Salesforce University's 501 certification site.And most important is to have patience. The 501 exam is a much slower process than 201 or 401. Although it's improved since I've taken it, it took about 9 months from start to finish for me, and I was able to get into the first programming assignment window.
Cheers, and good luck.