I got an email from a rock artist about this very thing... in her case, she was going into the studio and had rehearsed her songs so much she was bored with them. She recognized the trap and wanted to know what to do. Here are some thoughts I'll share with you as well:
Caution before we begin: no matter what you do, you must take care to use good technique when you sing. Don't tighten your throat or relax your breath support/control and strain your voice, no matter what.
- Rehearsal is NOT necessarily performance. You can rehearse a song, just trying out some different phrasing, style and licks and making sure you know it. You can do this all day long. This is different than rehearsing PERFORMANCE. When you do this, you have to "go on stage" and physically, emotionally & communicatively act as if you are. Don't do this more than a couple of times per song in a day. Give it a break.
- In the studio: Go for it the first time, or sing the song a time or two until you feel warmed up to it and the engineer is ready with levels. Then go for it. Don't expect to do take after take, however, and stay fresh. After about 3 or 4 good vocal tracks, I like to just start punching the bad lines. If it takes too long, come back another day instead of singing the life out of the thing!
- On stage: James Taylor once talked about this issue with his song "Fire and Rain" in a PBS documentary. He said when he and the band rehearsed it, they would all cut up and have a good time making light of the old standard. But each time he sings it to a live audience, he said it still feels like the first time. How? Because he lets the audience be a part of the equasion. He sings TO them, and their reaction feeds the freshness of his delivery. I'm paraphrasing him, but you get the point.
- Remember: Don't just sing. Communicate like it's the first time you ever said that to anyone. Know who you are as the deliverer of the song, know who you're talking to and why you're having the conversation.
- Passion rules. Keep the fire in your heart for your music, and it won't let you down.