Fanning your seam allowances involves spreading the fabric at intersections where multiple seams converge. This technique helps evenly distribute bulk and prevents bumps.
Here is an example of how to fan seam allowances on a four-patch block. All four pieces are sewn together and the block is ready for pressing. Click on the images for a larger view.
To fan the seams, unpick the last part of the seam until you reach the cross seam (indicated by the arrow). Make sure to unpick this section on the back side as well.
Unpick part of the seam, flip over and repeat on other side
Block with seam partially unpicked
Open the block to see how the seam allowances already point counter-clockwise, even before pressing (see arrows).
Unpressed block
Press the block carefully from the left side, and you are done. This is a simple trick to avoid bumps without having to press seams open.
Pressed block, note the tiny four patch in the centre