Step1
When entering a recording studio for the first time, it is not uncommon to be inquisitive. Though the enthusiasm is appreciated, it can, however, become distracting.
Upon your arrival, introduce yourself and quietly take a seat wherever you are directed to do so.
Step2
Unless you have a specific purpose there, please be advised that any input will be construed as unnecessary babble.
Please do not solicit opinions, unless you are asked.
This can become unnerving for those directly involved with the production.
Even though the artist may feel comfortable around you, it isn't always the best idea to offer an opinion when the artist may already be feeling a bit insecure. Having another opposing opinion will surely undermine the authority of the producer, who has been contracted to provide his opinion.
Step3
Please, be considerate of the production.
The last thing a producer needs is to worry about what the visitor needs at all times.
If you get bored, then step outside and get some air; go to the local coffee shop or grab a quick bite to eat.
The producer doesn't need to be catering to your every whim, while he is trying to perform his job. This becomes distracting and you get labeled a nuisance.
Step4
One of my personal pet peeves, is having people around other than the artist, producer(s) and engineer when recording a vocal session.
If you are not directly involved with the recording, then please, remove yourself from the control room.
To attain the best performance from the vocalist, she must be willing to let her guard down and expose her emotions.
Any third party will be considered a distraction and thus hinder the performance. Often just being within the line of sight with the performer can make them feel uneasy.