As a beginner, we hoped to be perfect immediately, so did I. However, your hand seems shake when you want to move and paint. As you can see, it is a trembling hand.
There are many reasons for this, but there are three main reasons why a hand can shake if there are no health problems that can be the cause.
Reason # 1: Do not put your elbow or arm on the table.
Of course it is a problem if you paint on the knee on the sofa. Although you seat by the table, please make sure there is enough space on the table to raise your elbow. You do not want to move across the paper when there are any obstacles on the table. Please reserve enough space for yourself.
Reason 2: Work with a small sketchbook.
As the sketchbook is smaller the space is less, so you will put your hand on a small sketchbook. Even if there is not enough space, the hand can slide and shake.
Reason 3: Hold the pen and brush strongly.
It will not fall out of your hand, loosen your grip and everything will be fine. When I get stressed, I tend to do this. So leave enough space to relax and work.
Also, enough exercise will help you to do better. Practice can help you become familiar with the brush and then creat muscle memory.