It might not look cool but try sitting with the guitar in a classical style position facing a mirror, lower your so elbow so there is a straight line running from your barre finger down your forearm,
It also helps to position your thumb in the middle of the neck behind the barre finger and squeeze/clamp the finger and thumb together this should eliminate any buzzing.
Other than that it really is just practise, hope this helps and let us know how you're getting on.