Time is money. Stars can get away with flubbing lines and needing retakes; we cannot. No matter how few you've been given, learn your lines by speaking them OUT LOUD. Learn how they feel in the mouth and on the tongue, and how they sound. After they're absolutely word and thought perfect and you know you can't possibly make a mistake, it's time to learn your lines. Then do it some more. Your responsibility is to know your lines, no matter how boring you find it practising them. BTW, did I mention it's important to know your lines?