Combine the proper portions of your diffuser base oil or dipropylene glycol with your essential oil or essential oil blend and mix well. I find that combining either in a bowl with spout or in a separate bottle works well.
Essential oils vary in strength as does the effectiveness of particular diffuser base oils, so you may find that you need to adjust the ratios a bit. If you are using stronger essential oils like geranium or peppermint, you'll probably want to use less essential oil.
If you are using thicker or more gently aromatic essential oils like patchouli, you may find that you need to increase the amount of essential oil used.
Use alcohol, as described under "Optional Ingredients" if you find that the thicker essential oils aren't wicking up the rod well.
Experimentation will be needed. Keep a notebook of the exact ingredients, essential oils and proportions that you used so that you can reduplicate your recipe the next time, or adjust it, if needed.
Pour your aromatic diffuser reed oil into your chosen diffuser bottle.
Add the rattan reeds to the bottle so that the ends are submerged fully in the oil. Rattan reeds can be cut if needed.
Every few hours (more or less) over the first day, flip the reeds and place the opposite reed ends back into the bottle. This helps the wicking process. After the first day, flip the reeds every few days.