Even if your experience doesn't exactly match a job description, you might be able to create a compelling case for getting the job. Perhaps you're lacking one or two stated requirements for a job. Imagine them as a gap between an employer's perfect imaginary candidate and you. Sometimes the gap will be significant, like requiring five years' experience when you have two. Sometimes it will be more flexible, such as requiring business travel when you've never done it (but could).

Since employers pose this gap as a set of objections to your candidacy, your job is to bridge that gap. This exercise will help you do just that.

Job requirement gap - A stated requirement in the job that you don't possess.
Possible objection - Why would an employer believe the gap would prevent you from doing a good job? If you can imagine the reasoning behind the requirement, you can bring it into the conversation, or discuss it in a cover letter.
Relevant experience (bridge the gap) - Experience or knowledge you can associate with overcoming the objection.
Support - Experience that helps your case. Numbers help a lot here.
Substitute - Introduce a substitute or parallel skill. For example: If large sales account management is in the job description, and you've done well in a telesales environment, step up and prove you've got the experience managing complex sales and building long-term sales relationships.

Of course you must be realistic. Two gaps in a job is about the maximum you can finesse, and if the gap is too wide (for example, if a legal certification you don't have is required), you shouldn't apply for the job.