By the time you work with a crew and directors, you should already have spent time on your own to memorize your lines. If you find it hard or a daunting task, then set aside time everyday for it. If you have a busy schedule, you should schedule blocks of time when you can sit down by yourself and rehearse your lines. Break up the lines into different sections that you can work on memorizing and set goals to memorize a specific amount by the end of each session.
Practice saying your lines out loud rather than just quietly reading them. This approach will help reinforce the lines as well as get you ready to perform with the proper inflection and nuance. Also, it will help you pick out patterns that will make it easier to learn other lines. Saying the lines out loud will also put them into context. By understanding when the lines are spoken within the play, you will not only be able to deliver them better but will also memorize them more easily. You can move around and practice as if you were on stage as well.
Look for cues within the lines that will help you remember what comes next. There are always a few lines that will be difficult for you to remember, so using other cues, like stage blocking or what other characters are saying, will help you remember what comes next. Also, you need to memorize a bit of the other actors' lines so that you know when it is time to deliver yours.
If you drive a lot, tape yourself practicing and listen to it in the car. This exercise will show you how you sound and what you need to work on; it will also reinforce the lines. You may be able to pick up on cues by listening to yourself in this manner that you may not have been able to pick up on otherwise.
Print out your script on the computer and make your lines slightly bigger and bolder than the others so they stand out to you. Also, highlight them in a bright color so they are easily found. You can highlight each character in different colors so you know who is saying what at a glance.