I use a special windscreen cleaner marketed by my son, under his own company’s brand name. It’s a spray on clear blue liquid, which rapidly softens dried on flies etc. after leaving it for a minute or two I wipe it off gently using a microfibre cloth.
I’m not mentioning the name because I don’t want to be accused of advertising and possibly breaking the rules of the forum.
That said, for years I used very diluted washing up liquid in a spray bottle and also used it on the company’s helicopter windscreens. Wiped it off with a synthetic chamois leather. There are “specific” windscreen cleaners for aircraft but many leave a waxy residue which can cause a smeared condensation pattern in cold humid weather, difficult to clear. That’s the last thing you want on a cold, damp, and dark night just as you lift off…