To start, you don't.
Start with vaping plain base. I don't care what ratio you like (I'm a 50/50-1.2% guy), start with it. Pick one flavor and add a little of that to a 5 or 10 mL bottle containing a measured amount of the base. Shake like the devil and try it. Let it sit/steep/age while you try another small batch with a different flavoring. Go slowly, and limit yourself to just a few flavorings for the first few days.
Over this time, continue sampling these mixes. Now you can begin to decide of you are too strong (add a little base ti dilute), or if you have mixed this one too weakly (if so, add another "bit" of this flavoring to strengthen it).
Once you get a couple of mixes that please you, try combinations of these two mixes...
Now, you are on your way!
For starters, here is a good guide to start with:
Use 20 drops of base. Then, adding flavoring at
1 drop = 5%
2 drops = 10%
3 drops = 15%
(Double the base amount and the percentages half, etc.)
Use the same device for all the drops to insure consistent drop size.
Keep notes. Try fruits first since they are the easiest to mix (less steeping times).
Don't be afraid to "try-it". Your only working with 15¢ worth of raw materials. That's about half the cost of one of those old Marlboro-Lights...
Welcome to some of the most fun available...
edit - One last piece of advice - > Read, read, read! Read the stickeys, Danny45's and Hoosiers' blogs. Then, re read it all again... Reading is the cheapest and most productive aspect of this hobby.