So i am want to start diy my own liquid and i think i try every flavor alone so i know there test and start to make my own recipe any idea how to do that? and what the percentage of the flavor to add and the steeping time
Yep, testing flavors as standalones is a _very_ good idea, IMHO. It might not be necessary if you purely follow other people's recipes, but if you want to make your own you need to know your flavors.
When I'm not being lazy I usually test at 2-3 percentage, cause flavors can change a _lot_ at different concentrations. Something that's pretty tasty at 2% might be quite unpleasant at 3%, and vile at 4%.
What percentages to test at depend completely on the flavor. 10% might make sense for a few (though I don't think I would ever start there unless I knew a flavor was really weak,) but if you try that with something like FLV Rich Cinnamon, or any really strong concentrate, you're going to have a bad time.
I think probably the best single source of information on good starting percentages is alltheflavors. Most of the people posting recipes there have at least some idea of what they are doing, so the averages aren't as likely to be thrown off by people mixing flavors at 30% as it is on some other database sites. So, for instance, if I wanted to get an idea of where to test FA Fuji (a concentrate I use a lot) I'd look here:
FlavourArt Fuji .
Looking at that page, I see that the average used is 2%, but that the average used in public recipes (which are likely a bit higher quality) looks a bit lower than that. So I'd probably try it out at 1%, 2%, and since it's a fruit flavor that's (hopefully) unlikely to get too weird at higher percentages I might also try it at 3% or 4%.
It also helps to know something about how the flavor is usually used. Fuji, for instance, is used as an accent to other fruits more often than it's used as a main flavor, which pulls it's average percentage down a bit. So it turns out that it doesn't get weird at 4%. If you search for recipes using Fuji and sort by rating you'll find that Fuji is used at 4% in the highest rated recipe there, in fact. So having some context for a flavor (which you probably ought to have before ordering it anyway) can guide your testing, and testing Fuji at 4% is probably worth doing.
EDIT: And, not sure how I left this out, this:
index/flavor_reviews - DIY_eJuice is also a very useful resource. Flavor reviews can only take you so far, since we all perceive flavorings so differently, and since each recipe has its own needs, but they can be very useful for things like starting percentages, etc.