Having difficulty at first in creating a barre F is normal (discouraging maybe, but normal). Learning how to fix common guitar barre chord problems can help you nail this vexing chord before you decide to give up on the guitar and take up the sousaphone. So, if you're having trouble forming barre chords, try the following tips.
Line up your left-hand thumb on the back of the guitar neck, between the spot where your first and second fingers are positioned, to give yourself maximum leverage while exerting pressure.
Instead of holding your index finger totally flat, rotate it a little onto its side.
Move the elbow of your left arm in close to your body, even to the point that it’s touching your body at the waist.
If you hear muffled strings, it means that your left-hand fingers are touching adjacent strings and keeping them from ringing. Try exerting more pressure with the fingers and make sure to play on the very tips for extra clearance. Calluses and experience help you get a clear sound from a barre chord.
As you start moving the chord up the neck, you'll find that you need to exert more pressure to fret at the bottom of the neck (at the first fret) than you do at, say, the fifth fret.