My first rotation has been in a large, renowned but chaotic lab. We're about halfway through the term, and I have been mildly successful.
There is but one overarching rule for any student in a lab such as this (or any lab environment, for that matter): be respectfully assertive.
This is an ubmrella rule that includes but is not limited to the following:
1. Make sure that you are actually trained before you are sent off to perform experiments and obtain data. It is a waste of everyone's time and materials (and dangerous if you are working with animals or viruses, etc.) to risk a new lab member collapsing an experiment because they were not properly trained*. Seriously. If your lab mentor is not up to the task, find someone who is or talk to your PI. You can do this respectfully, with the understanding that your lab mentor may be distracted or under an unusual amount of pressure.
2. Do not be afraid to ask questions and seek communication. This seems obvious, but in certain labs it is difficult to gauge whose office/bay you can barge into with questions at any time, and with whom you need to set up an appointment by email to drop by for a 5 min discussion. Find these details out early on in order to facilitate moving projects along. Anyone in your lab should be happy to help you, or direct you to someone better equipped to do so.
3. Your lab schedule will be dependent on the schedule of the person/people training you until you are self-sufficient. And even then, you may have to coordinate sharing space/equipment and assistance on certain procedures. Be respectful of the demands on the people training you, but do not submit to being trampled all over either.
In my current lab, not many people typically know what is going on at any given time. This is problematic as there is an extensive amount of sharing space/equipment, and many people participating in different elements of the same projects. It's something they're [we're] working on... little by little. It's something that I'm learning to navigate with mild success.
* experiments go awry often enough on their own without this variable aiding their demise.