How to address back talk

My fiancee and i are adopting her 8yo cousin to give her a better childhood. This is my first child, and ive been in the military for 8 years, so my way of dealing with back talk/disrespect isnt appropriate for a child. So what are some good methods you guys have used with your children to deal with back talk and questions when telling them to do things? via /r/Parenting http://ift.tt/29W3WLp