Step 1 - Thread the cable ties through the holes as shown. Make sure the heads of the cable ties face the back and the notched side of cable ties face out.
Step 2 - Position mudguard between the fork lowers. Wrap the cable ties around fork bridge and lowers and loosely cinch them up to get the placement just right.
Step 3 - Cinch up the cable ties firmly and be sure to rotate the cable tie heads behind the fork arch and to the back of the lowers. It just looks tidier.
Step 4 - Involves beer and admiring your work.