Use a gentle, oil and alcohol-free cleanser, preferably SBL Lash Poo
Keep in mind, if you sleep on your face, workout/sweat, and enjoy hot showers your lashes will shed prematurely. Also, taking multi-vitamins/medication can play a role in premature shedding as well.
The biggest myth is that eyelash extensions ruin your natural lashes. If applied properly and keeping regular maintenance appointments, your natural lashes should grow & thicken.