Many beginning axe pickers find the bar chord to be one of the hardest things to master. I doubt that anything I provide here will prove to be the "magic bullet" that will turn an accomplished "chorder" into a major bar chord talent, but every little bit helps. After all, the only way to ensure success is to, well, follow the tips offered below.

1. Don't give up.
2. Play the strings with your first finger lying across all six of them. Press down just enough so that you can hear each string minus any buzzes. Attempt to do this at or around the seventh fret. The closer you get to the first fret the harder it is to accomplish this as the strings tend to "get tighter". 
3. Once you've mastered the previous tip, move that finger (the first) up and down the neck of the guitar a fret at a time, each time checking to ensure that every note is cleanly heard - i.e., no buzzing notes and no muted notes.
4. When you feel comfortable with the three previous tips attempt to play a "real" bar chord. Try some of the examples below. The top two chords are major chords. The first is an A major chord and the second is a C major chord. The second row of chords contain, from left to right, an A minor chord, Am, and a C minor chord, Cm. The photographs below the chord diagrams illustrate the positioning of your fretting hand when playing a bar chord.

Bar chords are cool because by learning one fingering, you learn 12 chords. You see, in the case of the bar chords shown above, the lowest note played is the "root" or letter name of that chord. If I played the first chord diagram, top row, at the first fret, I would be playing an F major chord. This would be true because the lowest note in that chord shape is found on the sixth string, and the sixth string note value at the first fret is an F. 

For further reinforcement of this concept consider the chord diagram on the top row, left*. Its lowest note is found on the fifth string. If you were to play that chord shape with your first finger barring the third fret as the diagram shows, you would be playing a C major chord. This would be true because the fifth string is a C when played at the third fret. If you moved that entire chord shape up one fret, you would be playing a C# major chord because the fifth string at the fourth fret is a C# note. Sliding that chord shape up another fret (to the fifth fret) would yield a D major chord. Get the picture?

*This is one devil of a chord for most beginners. I cursed the inventor of this chord fingering the first day I encountered it too many moons ago. The barring of the second, third, and fourth strings with the third finger is tough enough, but ensuring that the first string is heard clearly beneath all of that is absolute torture. But not to worry, you'll get it - perseverance being the key. I taught many students this chord, and those that worked at it eventually mastered it - some within a matter of minutes, some within a matter of weeks, and those others, well let's just say that we found their boots and picks lying amidst the rubble of an isolated trash heap (oops, excuse the babbling). 'Nuff said. Now go practice.