For better sleep: a couple of drops of lavender essential oil.
For a pick-me-up, against fatigue and lethargy: either 1 drop peppermint and 1 drop eucalyptus, OR 1 drop geranium and 1 drop rosemary essential oils.
Anxiety/depression: 4 drops each of ylang-ylang and clary-sage, 3 drops geranium, 2 drops basil, 1 sandalwood.
Focus: Rosemary, grapefruit, basil, juniper, peppermint, sage or clary sage.
Memory and concentration: 1 drop basil, 2 drops each of rosemary and cypress. OR 3 drops each of rosemary and juniper, 4 drops clary sage.
Mental alertness: 6 drops eucalyptus, 5 drops basil, 2 drops peppermint