TJ:Purge injectors for better fuel economy

I was finding my TJ hard on gas. The local dealer said to purge the injectors and clean the throttle body. Here's my numbers after the first tank post the operation

This was city driving. Not bad eh! 97 TJ 6 cyl, 4 litre

Now, how do I keep those injectors clean. I do a lot of short trips. Any ideas?

Thanks Jimmy