The most important things to avoid:
1. Excessive heat. Keep indoor and especially domed or terrarium grown plants out of direct hot sun.
2. Low humidity. Keep well above 50%. If you live in a dry climate, you will not be able to grow these without a terrarium or humid enclosure.
3. Keeping your Venus Flytraps too wet for the amount of light it is getting. Plants that are kept too wet may rot. During the summer when kept outdoors, they can be kept very wet. Indoors they will require less water, but never let them dry out.
4. Excessive handling. As much as they may seem like pets, the more you handle them the more stressed they will be.
That are showing signs of stress are not necessarily doomed. They grow from bulbs, which store alot of energy for the plant. Leaves that have blackened and died are only leaves, and the plant can grow more as long as the bulb is healthy. The bulb should be a creamy white color. If the plant is really having a hard time, un-pot it and check for fungus or any rotting that may be occuring for various reasons. Dust the bulb with a fungicide and re-plant it. Even if most of the rest of the plant has died back, the bulb can still produce new growth. Some plants will die back quite a bit while acclimating to new conditions. Never give up on a Venus Flytraps plant until you are sure that the bulb has completely turned to mush, we have seen some amazing recoveries with these.