At least a week before you plan to record, start preparing your voice. Practice speaking out loud (any kind of reading), especially if you don't do much talking during a regular day. Reading the newspaper out loud will do. Start with shorter readings, then increase them. If you don't usually talk for more than a few minutes at a time, or very few hours a day, you should start sooner.

Your vocal cords are muscles. Like any other muscle, if you exercise it regularly, it is toned up. Set a timer. Start with 10 minutes sessions of reading out loud, and gradually add 10 minutes each day after that. Take a 5 minute break every half hour. Take a 10 minute break every hour. See if you can get yourself up to two hours a day. Keep something soothing, like tea with lemon nearby.

This is not a contest. If your voice feels sore or hoarseness develops, just stop. Give yourself a day's rest, then try again, cutting some time off the next session. Vocal strain is damage that can take a long time to repair.