I try a mix first in a clearo. You can pre-mix the PG and VG in your favorite concentration (why not).
Put in about a ML of base liquid (PG/VG) and add a bit of flavor. Add the flavoring using a small syringe (i.e. a 1ml syringe).
Add some flavoring, shake-and-roll to mix, try it. Add more, bit by bit until you figure out where the "taste-point" is (i.e. where you're getting the right strength, not necessarily the perfect taste). This will give you a rough starting point.
It's rough only because you will have reduced your original 1ml of base by the amount you vaped off, but it will give you a pretty good idea of where to start without going through lots of bad batches.
Once you have this ratio down, mix up 5-10ml, and then start adding "extras". Be aware that ethyl maltol is NOT particularly a sweetener. Splenda is better for sweet.
Do the extras the same way; start with a clearo of flavored base, and add in a bit of the extras. Sweetener, 1% saline, everclear/vodka,
etc.
This method isn't perfect; the liquid is un-steeped, and you need to mix it pretty well (and the wick will absorb what you add first, so you have to vape through that). But it will give you a great feeling of how the flavors work, and how the extras modify the taste. Since you're doing 0mg, you can tweak later batches by adding a bit more base, a bit more flavoring, etc. without worrying about how it affects the nic concentration.
It's the same way chefs learn to make sauces; taste it all the time. Pretty soon you can predict how a particular ingredient will work, and what's missing from a particular mix.
