When it comes to capturing a good vocal performance, this video says a lot. So much goes into getting a great vocal. A good headphone mix is also imperative for getting the best out of the singer. I have always been very fussy about creating good comfortable headphone mixes for the artists I record. The vocal mix is very important in these sessions as explained in the video.
Give yourself more space than you think you need, as this can allow for room to acquire new equipment. If your recording studio is in your home or at work, try to use interior rooms because there is less risk of outside noise entering the room.
You have also got to get them in that right mood and create the right atmosphere. All these things are so much a part of capturing that cracking vocal.