Some great advice above.
I remember when I first started to tackle the barres. I had a bunch of dead sounding strings mostly. I found that by reinforcing the 1st finger with the 2nd, the barre was easier to do. I also found that I could rotate the finger slightly so that instead of the fleshy side down, the side of the finger was down and it seemed to make that barre easier to get.
Of course, the more you play and work on these chords the easier they become as your body starts to do what it's supposed to do. Muscle strength and muscle memory play a huge part in getting that barre right without thinking about it. That takes time and lots of practice.
Not dealing specifically with barres, but any chord on the neck..... I remember the first time I realized that to be a proficient player I needed to be able to instantly jump to a chord with out thinking and without hesitation. That was a fun time. Lots of missed chords and dead notes.... but with time, and practice and perseverance, it was accomplished.
Start by fretting across all 6 strings. The open tuning of the guitar is a chord. So learn to fret it successfully. Use 2 fingers if needed. Make each of the string ring cleanly.... pick slowly across and listen. As you start into the barres with additional notes. you will realize that there are generally only about 3 strings that must be fully fretted. The others are not necessary to press all the way down since they are fretted by the "other" fingers.
Have fun..... build strength .... and play that thing.