Because legato is all based in the fretting hand – poor fretting technique is generally the cause of most legato problems.
I find, most of the time – if a student is struggling with legato they generally struggle with other things related to fretting, too.
Like everything, good legato takes time.
Legato requires a certain amount of strength and dexterity from the fretting hand which only comes from practice.
That being said – here are 4 things that will improve your legato playing and overall fretting.
1. Curve your knuckles and distal joints.
2. Keep your fingers inline with the frets.
3. Keep your thumb in the back of the neck inline with the 2nd finger.
4. Keep your fingers close to the strings.