1. I do not store my lipsticks in a warm setup, heat might either melt some lipsticks or just spoil them. I'm not saying that high end lipsticks are so fragile, all I'm saying is that prevention is better than the cure. I also store them in the dark, and I never keep more than the lipstick I wear in my handbag. Your room temperature should be fine as long as it is not always exposed to the sun, or that you dont always have a fireplace that is always burning in your room!
2. Do not let a lot of the lipstick show out of the tube while you're applying it. Lipsticks are essentially not super hard and unbreakable, and if you twist out more than necessary, you're giving the lipstick more room to break.
3. Do not leave your lipsticks in your bag, at least not ones that you are not wearing. First and foremost, the temperature is uneven, and during the summer, the heat might spoil your lipsticks. Other than that, out of sight is out of mind, and you do want to use all your lipsticks. Lastly, generally speaking, the bottom of handbags is one of those filthy places in a woman's life, and having my lipstick in a dirty environment makes using it seem unappealing and off putting, and sometimes the dirt will stick to the product.
4. Do not lend any of your pricey lipsticks to anyone whom you suspect might take them for granted and use them over products such as lip liners than don't even go with the lipstick shade, or they might do what situation #2 talks you against doing. Not to mention that lipstick obviously touches your lips, and to let anyone just use yours is a little disgusting, in my opinion.
5. Try to use up a lipstick before 24 months, because I feel like that is the time that they start going really bad, smelling a bit sickly, and feeling quite horrible! And if you buy a shade you don't like and don't see yourself wearing that much. just give it to someone who will, because otherwise, you'll be throwing a pricey almost untouched lipstick straight into the bin, and that hurts!