Polymer Clay is durable and will bend if properly baked. This being said, DO NOT BEND your pieces unnecessarily as this does weaken the polymer bonds.
Do not wear polymer clay pieces in water. Brass charms and gold-plated charms tarnish much faster when wet.
Do not store polymer clay pieces in places where they could be crushed, such as a pocket or a bag. When put under enough pressure, pieces can snap.
If clay does get stained or dirty, you can use a q-tip and a little water to clean. if this does not work use a tiny amount of rubbing alcohol and rub gently.
Brass charms do tarnish over time. You can use a little bit of ketchup and a q-tip to polish, but be careful to not get it on the clay as it may stain it.