Fuel Injectors should be inspected and cleaned every 3 years or every 45,000 to 50,000 miles whichever comes first.
I have my fuel injectors cleaned every 3 years whether or not I've went 45,000 or 50,000 miles as it helps to keep the engine running smooth and prevents problems.
I also add some fuel injector cleaner to my gasoline tank after every 2 tank fulls of gas so after I use one tank of gasoline and then fill the gasoline tank up a second time I add a bottle of fuel injector cleaner to the gasoline tank.
That helps to keep the fuel clean and keeps the fuel injectors cleaned as well so it prevents problems as well.
I like to fix things before there is a problem which could create a breakdown on the road which is not fun.
Same goes for heater hoses and radiator hoses, belts etc I replace them before they go bad enough to fail on me.