Try inhalation before applying essential oils topically. Most of the time a headache/migraine can be best helped with inhalation alone.
A personal inhaler is going to be more effective than a diffuser, due to its intensity.
Keep in mind that some headaches, especially migraines, can get worse with (lengthy) exposure to aromas like essential oils, as well as (bright) lights and (loud) sounds.
Also be sure there are not simple fixes, such as drinking a glass of water, as many sources of headaches, other than stress, is dehydration.
Use topically if inhaling won't cut it, or if you have a throbbing/pulsing sensation. In this case, massage the essential oil blend into the scalp, temple, or the site of throbbing.
The massage blend and roller bottle recipes are provided at a 5% dilution, but a higher dilution (up to 20%) may be necessary. Always start with a lower dilution.
I've formulated recipes based on the best essential oils and the best methods of application.