Just play around with your flavours. You might get a nice surprise. If the concentrate is a dark colour use only a little, if it's light use a bit more. Start off with single flavours or combining 2 or max 3. Once you've made a few decent ones try experimenting with more complex mixes if that's your bag. To me it's all a bit poncey when you start having seven different flavours at 0.15% of this 0.38% of that etc. Unless you have the taste buds of a cockapoo you're only kidding yourself that you can appreciate the aromas and nuances of the difference between the inhale and the exhale.