Not a foster parent, but a 15 year veteran (12 with the State of Illinois) as a caseworker managing foster care cases. I also do training for foster parents just beginning their journey.
First of all, thank you for making this committment. We NEED good foster parents who will show our kids that abuse/neglect is not the "norm" and they deserve a better life.
Some tips: keep lines of communication with your worker and licensing worker open. If you're not happy, not getting what you need, not getting calls returned, don't let it sit and fester. Call the supervisor immediately and if that doesn't work, go up the chain of command. We lose so many good people because of miscommunication.
Go with your foster children to doctor appointments, counseling appointments, court, whatever. They need your support and because you are with them 24/7, you are an excellent advocate for them. When the Judge asks you how things are going, be honest--even if that means telling him/her that the caseworker is not doing what they are supposed to, i.e. giving you critical medical information, etc. (BTW, in Illinois, it is in the Foster Parent Law that all medical, psychological, behavioral information ABOUT THE CHILD has to be disclosed to the foster parent. To omit this information would not only be against the foster parent/worker partnership, it would be against the law!)
Know what you're willing to deal with. Sometimes you get a call in the middle of the night and are so excited that you may get a foster child that you forget that you don't necessarily want to deal with some behaviors/issues. Have a list handy so that you remember what you will and will not deal with--and stick to it. I would much rather have a foster parent tell me no (even at 2am) than have me move that same child a week later because they really didn't want to deal with the child's specific issues. Coming into foster care is traumatic enough, but a disrupted placement compounds the issues for the child. Don't be afraid to say NO!!! Don't worry, we'll call you again. Unfortunately there are way too many children who need placement.
Remember that even if the birth parents have done horrible things to their children, the children can still be bonded/protective of the parents and may actually BLAME you for their being in foster care. With patience and sometimes counseling, children work through these issues. Also, parents still have parental rights until they are terminated. Therefore they have a right to visitation. To protect your privacy, don't start these in your home. If after time you meet the parents, feel comfortable with them, whatever, it is up to YOU how much you want to disclose about yourself. But remember that these folks have done something to have their children removed and you do not want to be a target of their wrath through harassment, etc. Also, EXPECT to be hotlined yourself. It is not unheard of for biological parents to feel so completely angry and out of control, they figure the best way to "get back" at someone is to hotline the foster parents. KNOW YOUR RIGHTS. In Illinois you have the right to have an attorney, friends, family, whatever, present when the investigator comes out. DON'T PANIC!!! We in child welfare EXPECT foster parents to get hotlined. We are required by law to complete an investigation. However, investigators are well trained to find the truth in allegations. I know its hard when you're under the microscope to remain calm, but we're there to help, not hurt (Do No Harm).
I know there's so much more, but I've already taken up way too much time. Making this committment is HUGE in a family's life, but we NEED good people so badly. My best to you and your family in this endeavour.