Weird, I thought I replied on your comment already... if this is a duplicate, sorry about that
Basically, you would draw the dynamic line first, but in reality you kind of draw both the dynamic line and the drawing simultaneously. Neither are fixed or absolutely right, you just compare the two together and make adjustments when necessary.
In other words, you can draw the line of action first and then start drawing the character. If it seem that the line of action doesn't fit the pose, you adjust it. If the pose doesn't seem to contribute to the line of action, adjust the pose. As you see, you may end up adjusting both of them. When it's appropriate to fix one or another, is whole different matter. For that you will need that practice
Though it's not just simply about draw, draw and draw. You will need to do a lot of research on reality to understand how things really work and why we humans find some things (such as dynamism) more appealing than others.