Here is a simple practice track for practicing improvising in a C major scale. The chords are
|G |Am |Bm7b5 |C : ||
It is suitable for any player who can play the C major scale! When you are playing, see if you can listen to each note, and pick out notes which go with the chords.
Playing the guitar is about making the most of what skills and techniques you have, being musical with the things that you CAN do. Don’t worry about things you can’t do – just focus on what you can do, and be as musical as you can. The more you play, the range of things you can do increases – especially if you have a good regular practice routine.
As an example, here is a melody part for the same progression played entirely in first position, using only one octave from the G string up to G on the top E string:
So be as musical as you can with the skills and technique you have. It is a good habit that will strengthen your playing as you continue to improve your technique and skill level. And don’t forget to have fun!