If your problem is with the barred 1st finger, try to tilt the finger slightly towards the nut. The finger should not be flat down. Also, try and ease pressure of the middle of the finger, only the 6th, 2nd and 1st strings need to sound clear, as you fret the other strings with the other fingers.
If your problem is the other fingers, practice an open E Major chord, but switch your 1st finger for 2nd finger, your 2nd finger for 3rd, and your 3rd finger for 4th. This will allow you to get used to the finger positions of the 6th string major barre chord.