When you’re in the process of determine how best to perform any given working, consider carefully the nature of each and every ingredient you choose. If there’s an herb or oil or incense, think through the point of the chosen ingredient. What is it meant to achieve and how does it harmonize with the other ingredients of the spell.
There’s a reason for everything used, so if you’re going to make a substitution, make sure is the right substitution. Changing the number of ingredients doesn’t matter much (unless the number of ingredients is part of the spell), but using cinnamon instead of cumin or mugwort instead of wormwood isn’t always the best idea.
These associations exist for a reason and this needs to be understood and upheld if you’re to do effective magic.
Have a wonderful day.