Originally Posted by: tanhongzhi

My guitar''s neck kept moving whenever I change chords and I can't find a stable position to hold a guitar steadily without it moving so easily when I change chords. I have tried putting my right foot on a box about 20cm tall and the neck is still moving a lot when I change finger positions.

What kind of guitar? Are you using a strap?

This is primary function of a strap: to hold the guitar in place so you don't have to. Your hands & arms have enough to do playing notes, they don't need to do "double duty" & also hold the guitar up or in place.

Another thing to consider is how much force you are using to fret the notes & strum. Often beginners use a great deal of force & tension because it's difficult at first. But the more you practice the more you will see that only a minimal amount or force & tension is required. Any more is wasted effort & hinders your ability to play the guitar.

I have a tutorial for beginners that addresses how to hold the guitar for optimal fuctionality.

https://www.guitartricks.com/lesson.php?input=13958

Hope that helps.