You should alternate the direction of quilting. I start at the top center and work out. This means the center line of quilting goes down the quilt. The line next to it is going to go up the quilt. Simple flip the quilt so you can do this.
You alternate each line of quilting. Same as when you quilt horizontally. Start in center of quilt and work out.
One line goes "east" and the next line goes "west". Hope that helps!
You also want to smooth the quilt sandwich outwards from prior quilting lines with your two hands on the quilt.