1) Be open to all types of adoption at first, then as you research, you can begin to knock things off your list.
2) If you already have children, plan to adopt children younger than your youngest child. Except in specific situations, it's best to adopt in birth order. This, in itself, will limit your adoption choices.
3) To begin your research go to your local library and find a good, comprehensive book on adoption. Actually, you might want to consider getting 2 or 3, to give you more perspectives. Don't both reading the legal stuff at this point, because laws change and vary state-to-state. Even paperwork changes. It's a waste of your time to read it now.
4) Call local adoption agencies. Many offer a class on types of adoption. They should also be willing to send you information on their services, and, if you are interested in international adoption, be willing to recommend international agencies they have worked with.
5) Check your local county Job and Family Services. Not only do they have many children needing families, they often offer free training classes where you can learn more about domestic adoption.
6) If you are considering international, think about cultures you are interested in, enjoy learning about and can present positively to your child. Then check with the State Department (see link under addition adoption resources) to see if that country has a working adoption program.