One of the first things I learned about dealing with galleries is that they pretty much all use what is called a consignment agreement.
This is the governing document and while it is not called a contract, it's a contract. So it is important that this document reflect the understandings, not only of the gallery itself but those of the "artist" (you) as well. Most times, the consignment agreement will be very heavily weighted in the gallery's favor. It will fall upon you to make certain that your interests are protected by this agreement. Whatever you discussed verbally with the gallery and/or agreed to must be reflected in the consignment agreement.
There are a few concerns you may have (or should have) that may not be covered in the consignment agreement. For example, how long the gallery is entitled to hold your pieces without selling them. Does the gallery lend or lease pieces? If so, how do they compensate you? Is there any specified time frame in which the gallery must notify you of the sale of one of your pieces? This is most important because, unless the gallery is within easy walking distance you are not likely to be dropping in to see if any of your stuff is gone. I had one gallery employee tell me that it was unadvisable to place work in any gallery that was far enough from you that it would be difficult for you to keep an eye on things and see when pieces were sold.
It is important to remember that galleries cannot exist without your work. They exist to sell your work. It may be true that the gallery offers a walk in showroom for your work that you might not otherwise have. And exhibiting your work in a well known and respected gallery may give you a certain prestige. But you need to remember that you are not really working for prestige. You need sell your work and get paid for it in order to keep working. You are at least as important to them as they are to you.
As with any contractual relationship, what matters is what is written not what is said. You are under no obligation to accept terms that are unfavorable to you. You can negotiate. But you need to do it up front and make sure that everything that is agreed to is reflected in the written document.
It is also a good idea to have short term agreements that have to be re negotiated. The reason for this is that when your work begins to sell, you become more valuable to the gallery. And the more valuable you are to the gallery, the more favorable terms you will be able to get. Sit it would not be to your advantage to be locked in to a long term deal.