I have spoken with many abuse survivors. The first step is to provide a safe home environment. Make sure the people with your children - family or not - are trustworthy.
Second, train your children to touch others only in respectful ways, with permission, and to require the same of others. Teach them to be honest, even when threatened or scared, and model that to them.
Third, do not rely on overly-simple techniques such as telling your children not to talk to strangers. Sexual abusers know ways of befriending children. Instead, set up a secret password, and teach your children not to talk to any adult who does not know the secret password.
Fourth, as your children get older - 10 years and up - start to talk to them about healthy relationships, love, and sexuality, and explain the opportunities and dangers they face.