I am new to acoustic guitar . What is best practice for chords hand ? I want to improve my chords' hand speed .
Hammer-ons. Rather than putting your fingers on the appropriate strings/frets one at a time, try to get them down as a hammer-on. After all, this is how, hopefully, you will end up forming them when you are playing. All fingers need to land together and firmly.You sort of make the chord shape before you smartly land them on the strings. Of course it'll take practice time.
Second hint - there are many changes that occur frequently. Take open E and A. If you leave your index finger on 3rd string, 1st fret for both, it will act like a pivot, and the middle and ring fingers can move across one string each, leaving the pinky to join them on 2nd string, 2nd fret to make the A.Look for changes where you can leave a finger or two on the same place.
Third hint - be aware that there can, and should be two or three different fingerings for some chords, dependent on which chord precedes and follows. For instance, open D has 12 different fingerings, so find two or three that you're happy with, and change to and from D to see which work best.
Welcome to the wonderful world of learning to play guitar.
I think one of the must frustrating things for new aspiring guitarist in the beginning stages is learning to play chords. The strange and unusual shapes that your brain must get your fingers to contort into are unnatural and often very difficult in the beginning. Everyday life does not require your fingers to do anything like what you must do to form chords. Yet the ability to play chords is central to playing the instrument - because just about everything we do on a guitar revolves around chord formations.
One of the problems is that to play guitar and form chords, you must develop finger independence. Most folks start out with one finger wanting to drag another along with it - but some chords require them to go in opposite directions.
One exercise you can do to help develop finger independence is to lay your hand palm down on a table and lift each finger (excluding the thumb) one at a time while keeping the others on the table. Then do the same but lift two at a time, alternating through all the possible pairings of fingers. Finally lift 3 at a time in each of four combinations where the fourth finger would remain on the table.
Another exercise for finger independence would be to start with all of your fingers together and then make a scissor clipping motion first using your index and middle finger, then your middle and ring finger and finally your ring and little finger (pinkie).
These exercises can be done even when you don't have access to your guitar and will help your brain learn to control your fingers independently. It's difficult to do at first but eventually it gets much easier.
As far as learning to form the actual chords, Tim made a great point in his answer about choosing logical chord formations that help you make common transitions without having to lift all of your fingers off the fret board.
To further illustrate the idea that there are different ways to form the same chord - click here 5 ways to play an open G to learn 5 different ways to play an open G that don't include any barre chord voicings of that chord.
After you decide on a chord formation that works for you that you want to learn, you will want to practice forming the chord until you can basically form it in mid air before your fingers land on the strings. In the beginning, you might start by practicing just hitting two of the three or four strings called for in the chord. Place your fingers simultaneously and then straighten them and then place them again. Do this over and over until you can do it quickly with two of the fingers. Then do the same thing using two other strings (maybe one of the same fingers while bringing a third into play). Finally, practice forming the entire chord and hitting all the strings with all the fingers at once then straightening your hand and repeating until you can do it reasonably quickly.
Once you are able to form a chord quickly and straighten your fingers and form the chord again, learn another common chord that fits with the chord you just learned (part of the chord set for the same key). So if you just learned to play a G chord for example - you might want to learn a D or a C chord next - as these are the two most common chords besides G that you find in music written in the key of G.
One you learn two chords in the same key, practice transitioning back and forth between the two because in the real world of playing guitar, that is what you will be doing often.
The most important thing I want you to understand is that it is natural and common and normal for it to be difficult to form chords in the beginning. It is a slow process but once you begin to learn a few chords and start playing a few two or three chord songs, you will further the development of finger independence and it gets easier and easier to learn more chords as you go.
So realize that it will take time and there will be great frustration in the beginning. But if you stick with it, you will be playing your favorite songs before you know it and you will be on your way to a life long skill that will provide countless hours of enjoyment. Enjoy the journey!
In addition to the other answers, you need to look at your ergonomics, which will not only improve speed but prevent injury. Musicians are small-muscle athletes and get injured without proper technique and warmup.
Press a chord voicing on your guitar with your fingers as close behind the frets as possible. Playing one string at a time, lighten your finger pressure until the string no longer sounds. Now press very slightly until the note sounds again. This is the finger pressure that you should use when you press chords. You will slow down and hurt yourself if you get a death grip on your guitar neck. For every chord shape, play each string to make sure that the string sounds cleanly. If a string does not ring, then adjust your finger position not your finger pressure.
Fret chords with your wrist as straight as possible, even for barre chords. Cranking your wrist at a sharp angle pits your fingers against your wrist. You don't want to fight yourself. Angling the guitar neck up and making sure your thumb is on the middle of the back of the guitar neck helps. Keep the thumb relaxed. You can actually fret chords without your thumb on the neck at all, it's just a convenient anchor. Keep the guitar in position by pressing the elbow of your picking hand on the body of the guitar, not your grip on the neck.
Learn the open position chords next to the nut first. Then learn to play power chords. Then learn barre chords. Open position chords you will learn to play without even thinking about them. Power chords are for when you know the root of the chord but can't finger its major or minor form. Barre chords are for when you don't have an open position chord for that chord. Bb major, for example.
Go forth and do good!