A good playing position is essential to good, comfortable playing, but finding that position can involve trial and error.

However, the 'classical' position generally works best when sitting, although using a 'dreadnought' or 'jumbo' folk guitar makes this impractical.

With a standard classical guitar, sitting on a straight chair or stool, you would need a footstool (adjustable) under your left foot, with the guitar supported on the left leg.

The 'nut' of the guitar would be roughly at shoulder height, and the right upper arm would balance the guitar to prevent it moving when playing.

You haven't said which elbow/shoulder is causing the problem - my guess it is the right (assuming you don't play 'left-handed').

Most people have some discomfort brought on by playing, and there isn't always a solution. But you can go some way to minimising it.

If you play a 'jumbo', classical position doesn't work, you have to compromise. A shoulder strap is necessary, but it should be attached to the body of the instrument, not the top of the neck!!

Few 'jumbo' guitars are made with a strap button fitted where the neck meets the body - but I fitted all of mine with them. The strap then supports the instrument which is now on your right thigh instead of the 'classical left'.

Whichever method you use, the right arm should move mainly from the wrist when strumming, with just a little elbow movement. If fingerpicking, the elbow shouldn't move much at all.

I always taught my pupils to hold an imaginary orange (a real one at first!) to position the right hand fingers correctly, so they all 'present' to the strings at the same length; the thumb should pass outside the index finger as if tightening a wing nut (butterfly bolt?) to avoid collision!!

Phew! Don't I go on!!