The National Association for College Admission Counseling (NACAC), founded in 1937, is an organization of more than 15,000 professionals from around the world dedicated to serving students as they make choices about pursuing postsecondary education. There are many resources on their website.  Here are links to a few that are particularly helpful.

Preparing for the College Application Process
Searching for Your Best Fit College
Applying to College
Making Your Final Decision