How often should you re-apply for credit?

Inquiries remain on your credit history for 2 years, and will affect your scores and ability to attain credit. Mortgage and Car loan inquires are a little different: the bureaus allow for "shopping time" so that multiple inquiries of this type of credit only count as one as long as they are within the same 30 day period. Usually when you are declined credit, they give you specific reasons for the decline. Fix the reasons before re-applying, otherwise, you will just be shooting yourself in the foot with added inquiries.