They are called bar chords (when your index bar's the strings) and they give every guitar players a hard time when you first start to practice them :)

The only trick is to practice practice practice.
But I might have a quick tip to make thing easier for you. You probably already know waht I'm gone say but its worth mentionning, just incase.
When you play chords, your fingers must press the string with the very tip so you dont mute strings here and there by accident. The best way to achieve that is to lower your thumb behind the neck. The lower the thumb, the bigger the "arcs" the fingers make to reach the strings.

Good luck and have fun with your learning