So I just got into DIY a while back and it seems that every time I make a juice the flavor is just kind of weak. I'm currently using TFA green apple, blueberry candy, and kiwi. At first I started with 10% flavor but that was way to little, so I moved up to 15%, while a little better I could use more flavor. So I'm thinking 20-25% next batch? Is this a normal ratio for fruit flavors?
Also, I bought the flavors stated above from wizard labs and was wondering if anyone knows where else I can buy flavors, preferably cheap

the shipping for wizard labs is a bit pricey if your buying in bulk so unless I plan to buy a slew of flavors I'd rather try a few different ones here and there from a vendor with cheaper shipping.
Just began reading this thread... are you steeping your mixes for a couple days before trying them and then quickly adding more flavor? I find when using Capella's concentrated flavors, I use about 5% of the total mix (in mls of the flavor(s), and 20% of the total mls for my 12mg nicotine, and then I figure how much PG and how much VG to get my choice of that mix in the total batch. Then I shake it up and let it sit 4-5 days (sufficient for Capella's flavors to blend nicely and fully). Another thing to remember is different brands (The Flavor Artist, Flavor Art, Loranns, Hangsen, Capella's, etc.) and strengths/concentrations of flavors can take more or less time to mix and mingle and flavor the base PG and VG... I find Lorann's (non-super-concentrated) to need sometimes up to 25% of my mix to taste like it should (after 2 wks of steeping), where as Capella's or Hangsen's to be down around 5% of the total mix (and good after 4-5 days of steeping). So, there are some other factors to keep in mind (and learn) as you DIY some e-juices...
There's a lot to learn, but here on ECF, are SO MANY folks who are more than willing to help you with any questions - k? The only 'dumb questions' are those NOT asked. (grin) I'm about 9 months down the road and have much better results these days with my mixes! Tho, I got a new flavor the other day and mistakenly added my nicotine amount measured in a needle, twice - so then I had to add double the flavor and PG and VG to my original 10ml batch - haha - got distracted, I did! So, don't beat yourself up too bad as you learn the ropes!!
It also helps to keep 3x5" cards on the things you do, so if you want to repeat it at a later date, you have the notes to follow.
Opps, one more comment - if 5% is suggested of a flavor, begin with say 3%, let it sit, try it, add some more, let it sit, try it, etc. and work up to what you like (after steeping). This takes time, but sure saves some money in the process!! keep that in mind
Many juices you buy already to vape are mixed as you order them and ALSO need steeping before they're 'good to go' - depending on what kind of flavors they use - might take 2 weeks, might be just 4-5 days...
I wish you well in your 'lab' haha Stay calm and vape on!
NancyB