Not much is required given how tough these things are. Polycarbonate is stable at a wide range of temperatures and can take a lot of abuse so don't worry too much.

Avoid leaving your boomerang on the dash of your car in high temperatures. It will probably be ok but it's best not to. Don't throw your throwstick at sharp or hard objects on purpose. Hardwood trees tend to be the most dangerous objects to strike, even more than boulders, since the bark traps the edge on impact. Polycarbonate can take a lot of abuse, generally, but it is never good for it and it can fail in time if thrown at hard and solid targets repeatedly. Throwsticks are designed to strike game and soft targets, not boulders, steel posts and hardwood tree trunks.

Don't aggressively try to warp or bend your throwstick or you may possibly change the tuning (unlikely). Moderate bending won't harm it at all, so no worries there.

If the edge develops a deep dent from a hard impact on a sharp/hard object, you may hammer this out to a degree on an anvil, if necessary, staying as minimal as possible in the area you affect. But avoid using a rasp or sandpaper on your kylie or you may change the tuning. Using fine grit sandpaper around the edges is ok, but on the surfaces will cause alterations in tuning if done over a large enough area. A small stone makes a great edge sander in a pinch, when small dings or scratches are formed, but be minimal with anything you do in order to avoid altering the tuning too much. Just use common sense and you should be good.

In sub freezing temperatures be all the more careful to not let your throwstick strike hard objects, as it is more prone to shattering at these temperatures. Polycarbonate is very tough and takes a lot of abuse over time. Because of this, \when it fails it does so in a surprising way. A stick not subject to abuse should generally last a very long time.

Polycarbonate is chemically sensitive. Various paints or other harsh chemicals may damage the material if exposed to them. We paint our sticks for our customers using acceptable paints. If one wishes to do their own dot art, this would not generally cause damage to the material, but it is good to be aware of this characteristic of polycarbonate.