If your roots get to long you risk breaking them off when planting. I usually get them about 1/4 inch in length.

Water them well after potting and if they wilt you will need to put them back in a humid environment for about a week until the roots take hold. I use a big clear plastic tote from Wal-Mart with a bowl of water inside. After a week I take them out and if they wilt, I put them back. You can also put them in a big zip lock bag if needed and poke holes in it every day to gradually get them used to the environment.