Dry newspaper or blue roll. Anything you are going to squirt on doesn’t make the dirt vanish – its just going to move dirt around until you finally get it off with dry paper so skip the moving it around bit.
The real trick is to able to see that you’re achieving anything. Its in particular light conditions that you can see the dirt – low sun – headlights of other cars etc. Give it as good a clean as you can but keep the cleaning stuff in the car on your travels and do the job properly when you can actually see the dirt.
The outside of the screen usually benefits from a good clean too and you’d be surprised how much black gunk is on the wipers.