The glib answer is "start a business." Seriously, all entrepreneurs need to know some marketing, whether they call it that or not. Market research, communications, advertising, and so on.
Do you have a specific recommendation for a high-value source of information (web site, book) about marketing for small businesses? Market research, managing marketing campaigns effectively, and so on.
to better understand your own flaws and root issues in business - read "Integrity" by Dr. Henry Cloud
to understand what you need to do in a start up - read "The Art of the Start" by Guy Kawasaki and "The Knack" by Norm Brodsky and Bo Burlingham and "Getting to Plan B" by John Mullins, Randy Komisar
Start with those books and apply the principles inside - yes, also start a business - and this will be a good start because application is key to learning.
hope that helps.