warning: elaboration from nomo means big ol' wall of text coming...

It's really easy to fall into the habit of just guessing where to start, but that's pretty inefficient. As a beginner, I'd strongly recommend that you first figure out a percentage range for each of your flavors that suits your taste. If you don't do this, it's sort of like mixing paint blindfolded. To speed up the process, it wouldn't be a bad idea to look around at what others have done before with any particular flavor; there are likely plenty of recipes with your flavors and several lists/spreadsheets to reference for range of use. If not, you'll just have to try your own range.

Here's what I've been doing. I take 5 small bottles and mix up 3-5ml of base with a range of percentages... usually 5%, 7.5%, 10%, 12.5%, and 15% to start, if there's no other known info from the references I mentioned earlier. Taste them immediately and make notes in my recipe calculator...too weak at x%, secondary flavor profile at y%, good standalone at z%, too strong, etc. Maybe even more elaborate tasting notes like if the flavor begins to taste like something else once a certain percentage is reached. If they're all too strong, I'll cut them with base so I have a smaller, tighter range like, .5%, 1%, 1.5%, 2%, 2.5%...my calculator will tell me how much base to add to get there. If they're all to weak...well, if it takes more than 20% flavoring to get where I want, I pitch the flavor and look for a different brand.

Then I age/steep them, especially for creamy/custardy/tobacco flavors or flavors that have alcohol in them. I actually use a cheap Harbor Freight ultrasonic cleaner to expedite this process. After your steeping/aging process, whatever it may be, taste them again to see if the profile has changed....Smoother? Weaker? Same? Add the info to your notes, and now you have some baseline data for balancing your mixes.

I'd recommend adopting this (or a similar) methodology early...I went by the way of just copying and sometimes tweaking found recipes and now I have around 80 of my 100 flavors that I really know very little about, plus I'm mixing to someone else's tastes and not my own. It's a little overwhelming to think how long it will take me to test each one of the other 80 flavors, but if I'd done it as I bought them, I'd be in a much better place now.

Here's another way where premixing standalones has come in handy for me...when I've finished testing, instead of dumping my testers, I'll combine all of them such that I end up with a single bottle of "optimum" standalone percentage premix (by my taste, of course). If I mixed up 5%, 7.5%, 10%, 12.5%, and 15%, each at the same volume and I liked 10% the best, I could just add all of them together to get a final mix at 10% in one larger bottle. Combining to achieve a different percentage will take more math and adding additional flavor or base to achieve that, but it's doable.

Then, when I'm trying to develop a new recipe, I'll use that premix to quickly mix up several iterations of my recipe idea. Using your flavors as an example, I may have previously found that I like cranberry best at 6% by itself, bav cream at 10%, and mango at 15%. If I combine 1ml of each of these premixes, my recipe would be 2% (6%/3) cranberry, 3.3% (10%/3) bav cream, and 5% (15%/3) mango. That's a 1:1:1 premix ratio, right? My other 3 iterations might be 2:1:1, 1:2:1, and 1:1:2. Or if I already knew flavor I wanted in the foreground, I'd adjust my 4 iterations accordingly, maybe 3:2:1, 4:2:1, 3:1:2, and 4:1:2, or something like that. Your variations could be even more elaborate than that, especially as you add more flavor to the recipe...this is just a quick and dirty example.

Finally, you just taste and tweak the ratio you think is closest to want you like as you see fit. It's not necessarily the "right" way, but I find it to be a fast way to throw together several variations of a concept. The downside of keeping all your testers as a premix is that now you end up with a big bottle of premix for every flavor you have. So, if storage is a concern, maybe you'll just have to mix up your recipe iterations on the fly.

TLDR: Learn the strength and taste profile of your flavors and their standalone optimum percentage to facilitate more efficient recipe development. Also, don't fret about failures; we all have them...myself probably more than anyone. :)

Try FA marshmallow instead of em

It just takes a little while to find the flavor manufacturers you'll like best. I ordered several of the same flavors from 3 or 4 different flavor manufacturers on my first order...it's an ongoing process of elimination. The downside being...the only way to really know which particular flavoring is best suited to your individual taste is to try them all from different manufacturers. Luckily in my case I'm not a big fan of fruits/dessert. I mainly try out different tobaccos, vanillas, chocolates and creams...I've tried just about every flavor manufacturer there is, I use a few tfa flavors but mostly flavourart, inawera and hangsen...it'll come for you, just don't set your sites too broad on flavors...pick a few that you know you like and try several manufacturers for each flavor...their is a huge difference in quality and you'll know it when you find/compare them