You should handle your sunglasses with care. This means gently pulling on and off your sunglasses, and making sure you that you don't stretch or bend their temples. These bad boys are durable, not indestructible.
If possible, put them in a protective case before placing them in a bag of mixed goods. If you carry a tiny cross-body, too small for a hard case, wrap your sunnies in a microfiber cleaning cloth or soft fabric before tucking them away. This will prevent scratching and prolong their life!
To clean lenses, it’s best to use a gentle lens solution. Apply it to the microfiber cloth, not to the lenses themselves. Lenses in rimless frames feature drill holes, while lenses in standard frames have screw holes. If liquids constantly enter these holes, this can have an adverse effect in the long term.
If you do not have a microfiber cloth present, lukewarm water and a drop of PH-neutral liquid soap provide the best cleaning results (be sure to avoid soaps with any lotion or moisturizers in them since these can damage or smear the lenses.)
Apply a dab of dish soap to your fingertip, then gently scrub every part of your sunglasses, starting with the exterior and interior of the lenses, then moving on to the frames, sides, and nose pads. If your sunglasses have inset details, such as a cut-out pattern or raised logo, use the tip of a lint-free cloth or handkerchief to clean the nooks.
Take care of your sunglasses at the beach. Make sure to keep your sunglasses inside your beach bag while you're not wearing them, as the sand and sea water can cause major damages. Salty water is the biggest enemy of metal and anti-reflecting coating (this includes excessive sweating too) and the sand can scratch the lenses or get stuck between the frame and it is very hard to clean it out.
Never put them face down onto a surface. Scratches can be very annoying and they can ruin your lenses. Never place your sunglasses on the car dashboard, where heat is particularly intense, and take them with you when leaving the car parked on hot days.
Stop losing your sunglasses. That's it.
Try not to grab your glasses by the arms. Hold them by the bridge so you don’t bend the arms. People often put their glasses on by holding one arm, and over time the arm can bend a little. But remember, good glasses can easily be readjusted.
Hopefully these tips help you keep your sunglasses in top shape!