If nobody in your family or circle of friends has adopted a child, it can be difficult to broach the subject. There are a lot of misconceptions about the adoption process and adopted children in general, and talking about it will invite people to voice what they know. You'll probably be subjected to a lot of prying questions, too. Your family and friends are likely just showing their concern, but keep in mind that ultimately, this is your decision. You'll be the one raising the child, not them.
If you decide to adopt internationally, adopt outside of your race, or adopt a child with special needs, you'll probably get some additional -- and likely, unwanted -- feedback. Be clear and firm. Take this opportunity to educate your family and friends, and invite them to learn more. If they want to continue to be a part of your life, they'll have to come to terms with your decision.
You'll also get questions and comments from strangers after the adoption, so questions now will help you get used to handling them. It's just a part of having an adopted child. People may ask how much your child "cost" or say that he or she is lucky to have you. They may also tell you that you got off easy by not going through labor or ask about the birth parents. These types of questions and comments typically come from a place of ignorance and not malice, but use them as an opportunity to educate. Always keep your child's feelings and right to privacy in mind, and don't feel compelled to share details.