The best way to prevent Multi-Flex from lifting and chipping is by applying Commit before application and make sure your application is thick enough as well as properly balanced. If your client is a known lifter, you can apply two coats and warm the second layer up in your curing lamp (cure for 5-10 seconds). This will make the primer tackier and helps gel adhere better.
Next, file the free edge after you apply the gel. Filing after instead of before not only prevents you from doing a ton of filing, but makes the nails much stronger. If you need to do significant reshaping or take down a lot of the length, then obviously do some filing before. Otherwise, file and take down length AFTER you've applied the gel. Then, the key to preventing lifting and taking down thickness is to bevel the free edge. You'll take a file and file at a 45 degree angle to blend together the free edge and the product, strengthening the nails.
Above all, a professional grade lamp is essential for properly curing product.
If you are still experiencing problems our best advice is to take a class with our Master Educator  Tara Robinson.