Problems reaching notes, especially notes on the fourth fret of the 5th and 6th strings, are usually due to poor hand position. Shortness of reach is caused when the palm is held diagonal or perpendicular to the neck, when the thumb is hooked over the top of the neck, or when a finger, often the little finger, is held too far from the fingerboard. Review the diagrams below for the proper hand position:
Buzzing or muffled tones may be due to improperly set action, worn strings or frets, plucking too hard or poor finger placement. However, poor finger placement is the most common cause of buzzing or muffled tones for beginners. When fretting, place your finger next to the fret, touching it but not directly on top of it. Whenever possible, avoid placing the finger midway between the frets: this position buzzes easily and requires additional pressure to make a clear tone.
If you think something is wrong with your guitar, seek the opinion of your teacher or a guitar technician. If your guitar is new, your dealer should be willing to adjust it for you (adjustments are often needed for new guitars, especially inexpensive ones).
Sore fingers are sometimes due to an improperly adjusted guitar, but more often than not stem from excessive finger pressure. Here's how to find the minimum finger pressure: Place your finger against the string (next to the fret), but don't press it down to the fret. Pluck the string. You should hear a muffled sound. Continue plucking and slowly increase the pressure until the string begins to buzz. Hold the pressure there--let it buzz. The pressure needed to maintain the "buzz threshold" is very small. Now, press just hard enough to stop the buzz and break into a clear tone. This small amount of pressure, a few grams, is all the pressure you need when playing!