If you are looking from a position where this is your first book, then I realise that you may feel you can't negotiate contracts, and that you are maybe lucky to have had your book accepted. You're also on a high and believe me I know how that feels. The question will always be there - what if I say something and they turn around and say they don't want me anymore?
The other proviso is that I had contracts with Silver Publishing that meant nothing unless I was willing to use lawyers to fight my case to get the independant audit the contract promised, or to get books back when royalties weren't paid. Lawyers cost money.
KJ Charles gave a very informative speech on contract negotiation at last years UK meet. I wish I had decided there and then to discuss matters with a publisher on a more formal contract basis as opposed to the casual, don't worry trust us rainbows and unicorns level. But, meh, you live and learn.
So, bearing this in mind there are a couple of things that you should do before signing any contract for your book.
Ask existing authors. And not just one or two authors. Ask big name authors with the publisher you are interested in, ask the new author with the publisher, ask friends, ask readers. Type the publisher name into google, buy some of their books... just do your research.
This won't stop you falling in with criminals like the owner of Silver, or from companies who's finances crumble, but there are good companies out there with strong ethics and finances to back them up and who aren't all talk.
Bear in mind that authors chat to other authors all the time, and if too many authors are saying the same thing then you should maybe consider avoiding the publisher they have concerns with.
Come and ask me, I can give you my list. It's not a long one. ROFL.
Some publishers have incredibly harsh contracts that tie you to giving them your first born (small exageration). Some have contracts lasting seven years. Some want first look at everything you write. Some have auto renew, some have language that only a lawyer would understand. In all of this there is one thing to remember when you sign a contract - this is law and you are tied to the terms of that contract.
And don't expect a publisher to turn around and say, oh well, never mind, we know we let you down, or we did ABC, or didn't do XYZ, but there is no spirit of the law, so you're tied. As I was told by a publisher recently, this is business.
Remember, being an author is a business too. If things don't seem right, then they're probably not and if in doubt consult a lawyer before you sign.