Every six months or so I will throw an injector cleaner in. Something like seafoam or lucas. That's about the extent of it. I don't usually worry about it becuase fuel now a days has so many damn additives already.
(Walmart)Supertech 2 stroke oil w/TCW3. 1 OZ per 5 gallons of gas.
There are alot of claims about it. The only noticeable thing I can say from experience is that the engines seem to run quieter with respect to valve train noise(after about 300 miles after you start using it).
I have run it in my Honda accord, and my GMC Sonoma. I haven't tried it in my Mustang GT yet. I may or may not do it. I didn't find it to be a big deal whether I used it or not, but again, the engine was noticeably quieter with respect to mechanical clatter noise of the engines.
In general I'm skeptical on any miracal claims of any additives. I'm sure they do some good, but I think the claims are inflated.