Lenses scratch over time, plastic ones faster than glass ones. The coatings are the first to go, so you can use that as a warning sign to get a new pair ASAP. Try to keep them in a microfiber lined case or pouch, not just a random shirt pocket.

If you start seeing "starburst" effects around lights at night, it means the lenses most likely are scratched.

Only clean them with a microfiber cloth, and never dry. At the very least, breathe on them to have some moisture. Blow on them first to get rid of any dust that would come off easily. Avoid rubbing dust into them, even with the microfiber cloth. It's best to use a single motion from one edge to the other, ideally while pulling the cloth away so dirty parts don't get dragged along the lens (takes a bit of practice). Shake the cloth off after each pass. Goes without saying, but clean hands are required to keep the cloth clean.

If you really have to, you can put them under running water, but beware of corrosion in any metal parts (frame, hinges, screws). Shake off leftover water, then clean with a microfiber cloth. DO NOT use a hairdryer on plastic lenses or frames. Depending on the water hardness, it might leave mineral deposits behind, so it's generally better to avoid it. Rain is usually fine, unless you get into acid rain, or dusty rain.

Chromatic aberration is inevitable, so no point in fighting it or panicking, it just comes with the territory. With a good pair of glasses, whatever you're looking at straight ahead, should look fine though. If it doesn't, consider getting back to your optician for a better fit.

Random reflections and glare are a thing too. There are coatings to mitigate them, which makes sense for like driving at night, but you might get by without them, YMMV.