Pre-shave oil scent won't last very long - if you still want to add essential oils to layer on the scent - that's entirely up to you - such as with AOS products...so if you're fav shaving cream is lavender - then add some lavender essential oil
But to make a pre-shave oil you need a carrier/base oil and essential oils (optional)
Use one of the following oils as your base or carrier oil:Olive oil, Coconut oil, Palm oil, Sweet almond oil, Jojoba oil, Sesame oil, Grape seed oil
If you want to use essential oils - add 5-10 drops per ounce of carrier oil - start with 5 drops per ounce of carrier oil - add more if needed - essential oils are very strong and can irritate if you use too much - so better to start with less and build up!
Some popular essential oils are: Lavender, Chamomile, Ylang Ylang, Rosemary, Sandalwood, Bergamot
I personally only use almond oil - it's unscented and works wonders! I also prefer my cream to provide all the scent and follow up with an unscented ASB (Nivea Soothing ASB)
What I recommend is that you get the base almond oil from Bodyshop or any other similar shop - try and find a spray bottle (I bought one from Muji) - and fill the oil into the spray bottle - this provides you with measured quantities every time you want to use the oil - not too much not too little - one spray should be enough - if I have a short beard - I use two sprays - there's no need to use any more!
hope that helps
I follow the same principles but use Apricot Kernel Oil (similar to Sweet Almond) I then add an antiseptic and a conditioning essential oil.