Always use branded and quality products. You might be able to save some money on buying lower quality products but the cost of damage they can do to your skin can be far higher than the savings.
Always try to clean brushes and other supplies before and after makeup, each time you apply makeup on you. Do not just throw brushes in the bag and then pick them again for use without cleaning.
It is better for the hygiene aspect to sterilize the supplies. For example, if you have to use scissor or any similar tool, it is better to sterilize them before and after use each time.
Always keep your powder and other makeup supplies in their containers properly covered on the top. You might have a habit of just stuffing the makeup supplies in the bag and just throw them away until next use, but it is not a good habit.
You should not share your makeup supplies with any other person, no matter how hard they request. Remember, each person has a different grade of their skin sensitivity and by sharing your makeup supplies with others, you can put yourself on a considerable risk.
While applying makeup make sure you choose a safe place to keep your brushes and other supplies. You should not just leave brushes on the floor or the table top after one use, if you use them again without cleaning, you are putting yourself at risk.
Do not use any piece of cloth as an assistant to clean some unwanted makeup product off your face, while applying or after applying makeup. Only use brushes or other such stuff that you trust is safe for your skin.