Yearly. After age 40, yearly. Choose a doctor that you can relate to, will listen to your concerns and you don 't feel rushed.
Many considerations. There is no research to tell us how often you should get checkups, but once a year or so makes sense, mostly so you can keep up on new/changed recommendations. My health checklist 2012 is a good iphone app that lists the current evidence-based preventive recommendations. To find the right doctor or nurse practitioner, start with word of mouth, and then try them out until you have a good fit.