Before you jump into the tanning bed make sure you apply the tanning lotion they provide you with. It will help you block excess UV rays from penetrating your skin. UV rays can be harmful and that's why you don't want to overdo your session in terms of time.
A thumb rule is to start with a session of 5 minutes if you have extremely light skin. 7 minutes is fine if you are darker. Increase it by a few minutes every time and judge for yourself whether you can handle it without any harmful effects.
You can't get a 'faster' tan by lying on the tanning bed for longer periods. You can only schedule your sessions at regular intervals and leave the rest to your skin. It's true that some people get tanned faster than others, but it all depends on each one's skin type.
So how do 'schedule' your sessions? The best way is to do it thrice a week evenly spaced. Whatever you do, don't do two sessions within 24 hours of each other. It is not going to help you get a better tan; it will leave you with serious burns instead. 24 hours is also what the melanin in your skin requires to jump up to its new level.
Remember that as a beginner you need to be well informed of the safety measures. Do go through the tips given for safe tanning. Always listen to your body. If anything hurts just slide off from the bed. Do tell the attendant at the salon that this is your first time. You will be taken care of. Safety is more important than a good tan. Everything said about safety, the tanning bed is a great way to allow a controlled amount of radiation hit your skin. Go ahead!