The most important part for a pretty magazine is a high resolution PDF. Make sure that all texts are vectors and the PDF has a resolution of atleast 180 DPI.
You can further increase the magazine quality in the magazine settings. You need the AdFREE plan or higher for this.
First go to "Edit magazine".
Then scroll down to the "Player Settings".
Here you find two sliders, the "Zoom factor" and the "Quality".
Zoom Factor: Defines how far the reader zooms in when clicking somewhere in the magazine.
Quality: Defines how high the resolution of your magazine is (can cause longer loading times).