not to take away from the airflow points which are bang on, I say:
Do it how you practice. If you sit do practice sit to perform, if you sit at a piano to practice record there, if you have a guitar on your lap when you practice have it when you record (just don't play it if you are trcking separate)
You should be comfortable when you record. If you change things up and don't do what you normally do when you record, you won't get a natural performance and it will show in the recording. (man I wish I had figured this out before recording my first two little EP projects)
as always YMMV