I started slow by mixing single flavors tasting as I steeped, and then combined single flavors in my tank. Not exactly the same as steeping "together" but it gave me flavor building blocks to start with. I also tasted a lot of (storebought) juice and also read a lot of recipes. The thing is, the percentages involved, while you may get a sense of some things starting out with a complex recipe, you have no idea if it will suit your individual tatebuds or not. I tend to flavor on the lighter side and am a "reluctant" sweetener user. So, not only do all manufacturers tend to make many flavors at a "certain" strength (e.g. Flavor Art flavors tend to be on the strong side) you will juts also find your tastebuds will naturally gravitate to more, or less flavor.
I tend to not follow recipes a) I really enjoy creating my own now that I understand "my" flavors and my "tongue" but often a premade recipe may be to strong for me.
Having patience, especially in the beginning, will pay dividends as over time, you will figure out what your tongue likes. It can be good to either have some "one shot" flavorings on hand that usually don't require much steeping, so you can taste test them, starting at a "low" percentage and adding flavor if needed, to get a sense of the "percentage" you like for one shots while still having success. That can be useful (or keeping some storebought juices around as you start DIY) to cut down on "impatience" and to also get some early "success" at DIY with one shots.
I wish you luck. For me, patience and keeping my expectations low at first was helpful. I am happy to report that at least 90% of the time, I enjoy the recipes I make, an if I make an overflavoring "error" I can usually fix it. Go easy on the sweetener too, if you are using it. Sucralose, at least, doesn't need steeping, so if you need a note of "sweet" you can add more, shake, and vape. It's a lot easier than trying to dilute down a mix (which I have also done, LOL).
All the luck in the world to you, and I'm sure that you can do it.
Oh, also, keep COPIOUS notes... Of failures, and successes. Nothing worse than finding that perfect vape and realizing you don't know exact percentages or how long you steeped it, etc. As well as failures, or flavors or tastes you thoroughly disliked, etc.
Good luck!
Anna