I would suggest doing single flavor tests of each of your flavors to get an idea of how that flavor behaves. So for example, I will make 5ml tests of every one of my individual flavor concentrates at 3 different percentages. I usually go as follows
VTA, WF, RF, FA, INW, HS - (1,2,3% - sometimes I start as low as 0.5% and go as high as 5%, I use ELR to get an idea of what other people are doing and go from there)
OOO, CAP, TFA, PUR, FW - (2,4,6% - again I check ELR to get an idea, some flavors are really strong in these lines and I like to get an idea before I make a 6% tester of TFA Brown Sugar Extra and blast my tastebuds away)
FLV - I start at 0.5% and taste it, if it is strong I do 0.5, 0.75, 1, if it is a weaker one I do 0.5, 1, 1.5%. I do this with some RF, WF flavors as well.
I take notes on all of this stuff. Knowing my concentrates makes me a better mixer. Instead of blindly hoping something will come out good, I already know what my concentrates taste like on their own at certain percentages, it gives me a much better idea of how they will behave in a mix. I suggest if you plan on really getting into this and creating your own recipes, you start doing this, it will change the whole thing for you.