Lavender is one of my personal favorites as it is calming and soothing. My tip for nervous riders and horses this week is to put Lavender oil on your clothes or somewhere on your person. It may be good to dilute it with another oil if you're sensitive. By doing this, not only will you calm your own energy by inhaling, your horse will inhale the aroma too. Your smell will actually be calming to him and you'll smell great!
Here is a nice list from Aura Cacia on some others oils and what they help with. Try some different ones out!