Glass and clear plastics
Glass and clear plastics not only look better when polished to perfection, but also improve safety and visibility when well maintained.
Most glass surfaces can be adequately cleaned using a damp microfibre cloth and then buffed using a microfibre cloth designed for glass (lint free).
If you have especially smeary windows then glass cleaners are a good way of cutting through the grease and bugs to a perfect finish. Beware of overspray however, as some cleaning agents may be harmful to your paintwork or dash. If you choose a cleaner suitable for tinted windows, then the formula will be mild enough not to damage plastics.
Spray one side of a microfibre towel with the cleaner, then use the other side to dry and buff.
Clear plastics require more effort to keep clean and clear, as the softer surface is more vulnerable to scratches which will dull the shine. This can be seen on this rear light lens before (top), and after (bottom).
Plastics can be restored in much the same way as paintwork, and a fine polishing compound will allow you to bring the surface back up to its best. For windows and headlights, this can be done with a mechanical polisher, although be sure to tape up and protect the surrounding areas first.
These surfaces need to then be protected: you can use a plastic/glass protectant or polish on windows as this will keep good visibility. For headlights, rear lights and other light clusters you could get away with using a synthetic wax.