Perhaps the best advice is to keep renewing your flight instructor certificate. Did you ever notice how many airline pilots attend CFI revalidation clinics? I know and admire many older CFIs who have retired from other jobs, but still work as flight instructors. They cite many reasons for their continued efforts.
In the first place, they just enjoy it. I can't think of a single exception. These are people who made a living as engineers, corporate pilots, airline pilots, and, in some cases, full-time CFIs. But, no matter what else they did, they always instructed. They never really quit. They take instructing seriously, and believe it to be a very important--even somewhat noble--job.
They tell me instructing is more fun, simpler, and easier when you are no longer scrabbling for money. They have a reputation now, and usually don't need to seek out students. One such fellow was the late Tom Wardleigh of Alaska. Tom was much honored by many groups, including AOPA, and students sought him out. I met one pilot in Alaska who said he wanted to get a checkride from Tom, "just so I can say I got some dual from Tom Wardleigh."
Another good example is Judd Davis of Huntsville, Alabama. Judd was a full-time engineer and part-time corporate and charter pilot, but he has always instructed. Last time I talked with Judd he still had plenty of students, and probably always will.
Think about the advantages of being in demand. You can raise your rates and maintain high standards. You don't need to chase down marginal students who won't work at it, and you don't have to accept mediocrity in students. Most of these people have been fairly independent for decades, because they were always good CFIs. Because they were known to be good--and a bit tough--the lazy, sloppy students didn't go to these instructors, but instead sought less-demanding CFIs. The same is true today.
Remember that one day, you will be retired. Can you really think of anything you'd rather do than keep a few students on the side? It would give you an excuse to get out of the house and hang out at the airport. You would remain a respected person in aviation. Like Judd, you might find several corporations who want you as a standby pilot in some sophisticated equipment.
Hang on to that flight instructor certificate. You may want it forever.
Ralph Hood, an aviation speaker and writer, has been flying since 1971 and has more than 3,000 hours of flight time. He is a multiengine commercial pilot with an instrument rating. Visit his Web site.