I do things by the drop, into a small closable container. I have some very small 1/2 dram-type bottles I use for dosing out homeopathic remedies that I bought in bulk. I am using these now. They can be reused after cleaning with grain alcohol, which is the type I prefer to use for this cleaning of containers. Other types of alcohol have too many chemical additives blended in to them which can leave residues behind which interfere with the next blend of essential oils I will be mixing up.
I will record how many drops of each essential oil I used, the date so I know how long the mix has been marinating together (they do change over time, as scents do, especially plant-based scents). I work that all out in percentages, so I can later scale this up for my larger batches of soap. If I am feeling underwhelmed by a scent blend, I continue playing with it, adding a drop of this or that until I'm happy with it.
As
@Nona'sFarm said, it's not a perfect system, but it does work for me every single time. I've put together some very nice blends like this.
I find other citrus-type-but-not-citrus essential oil scents stand my hair on end...citronella *gag* lemon eucalyptus *gag* lemongrass *gag* But you may love them.
I love pink grapefruit, blood orange, lime....lemon I find to be incredibly underwhelming, unless in food...yes, I do use a drop here & there of certain essential oils in food. Far safer & healthier than synthetic flavorings.