I run ring free as recommended by Yamaha, and I use their recommended dosages.  I also mix in star-tron every few fill ups(maybe every 150-200gal+), I usually do not fill my tanks unless I'm running offshore to the canyon.  I usually put close to the amount star-tron recommends, but I am a little on the conservative side and usually go a little less.  I had done this on my 22' Grady since repowered in 2000 with a 200 HPDI, and have had no problems.  I also do this on my 265 Express with F225's.  It is a cheap insurance policy IMHO, I know some guys who ignore to do so and have had some engine problems, not sure if not using the products was the cause, but knowing what the problems were I know it sure did not help the situation.  I also do basic maintenance more often then the engine manufacturer recommends.  I change my spark plugs every 100 hours, and/or at the beginning of each season after my first few trips.  I swear plugs never work the same after you run the fogging fluid through them, I try to burn as much off as I can then put new plugs in.  When the boat is stored for the winter, I put a dosage of Star-tron, I also add a bit of Sta-Bil in to stabilize the fuel, Star-tron does so many things that I feel it will not stabilize the fuel well enough on its own for a winter layup.