Often when students are learning how to play the guitar the most challenging task is correct hand posture and physical position memory. Students quickly understand what chord shapes they should be forming but training the hand to actually do it quickly is a longer process. I regularly see students get frustrated with themselves because of muffled notes or buzzing strings due to improper hand posture. In general there are a few things that often cause this problem.
Firstly, the improper sounding of notes is often caused by the fleshy ends of other fingers in the chord shape muting or touching a string below and causing it to buzz or not sound. To remedy this problem you must be sure you are pressing on the string with the very tip of the finger, just as you would to press a doorbell.
Second, you must insure you are getting a very high arch to your hand and finger posture, never lay your fingers across the fret-board. To get this high arch slide your thumb down the back to the guitar neck and rotate your wrist outward, away from the guitar neck. This should give you a better angle to work with.
Finally, make sure you are pressing down with a decent amount of pressure. Too light and the stings won’t sound, to hard and you will fatigue your hand quickly. A good test is to form your chord, arch your hand, make sure you are using your fingertips and then pluck each individual string, making sure every note in the chord is sounding. This will allow you to zone in on problem strings. Once you have identified the problem strings adjust your pressure, grip and force and try again. Once you get all the strings sounding clearly take note of how your hand feels. Where are you positioning your wrist? How much do you have to squeeze? How does your arm rest on the guitar body? By noting these things you are cataloguing the experience for the next time you need the chord, soon it will become second nature.
Also, always remember when beginning on guitar, your muscles in your hand and arm are not used to these movements so make sure to take regular breaks and stretch your hands. The best thing to do is start by practicing these hand posture techniques 15 minutes a day. Remember, practicing guitar is a lot like lifting weights, you do a little each day to get stronger, it doesn’t happen overnight.