I put in 1/5 of a bottle of REDLINE SI-1 INJECTOR & VALVE CLEANER with every fillup (if I remember).
Whether it does anything good, remains to be seen. I don't think it will do any harm.
I read about this product on a Camry forum about 10 years ago where many of the members swore by this product so I have been using it on my vehicles ever since.
It's supposed to keep deposits from forming on the valves. The REDLINE SI-1 is supposed to do a better job of cleaning the valves and injectors than perhaps some other products.
Many say that you don't have to add any additives if you buy good gas. I use premium fuel exclusively and that is supposed to have all the additivies already in it to promote engine driveablitiy and longevity.
-TM-