The Application Process

I have seen quite a few posts from MBA hopefuls concerned about their low undergraduate GPAs. Most advice from all types responders (experts included) involves pursuing additional pre-MBA coursework in order to compensate for low GPAs and bolster overall applications. However, I think most future applicants (myself included) remain unsure about how to go about this. I, for example, certainly don't want to waste time or money trying to strengthen my application in ways which may prove to be ineffective. So, I propose the following questions:

Should a future applicant look into full programs (MS, Graduate Certificates, Professional Certificates), or just relevant coursework (individual classes)?

If full programs are recommended, is there anything specific an applicant should be looking for prior to entering the program? Perhaps an applicant should verify the credibility of the program, but how?

If individual classes are sufficient, should an applicant aim to make up for subject matter which appears lacking in their undergraduate transcript (IE, try to make up for a C in Accounting by taking a graduate accounting course)?

Where should courses be taken? Are there any institutions which should be avoided, such as online or for-profit universities?

Thanks to all in advance, sorry for the long post.