I've done clones of some of my favorite retail vapes that have come very close but to be honest in my attempts to do this I've also come up with many I like much better then the original retail versions. How it's done is mostly by trial and error and searching the forum for post from others that have attempted the same clones.
The most important thing is to keep careful notes.
Same here. I get to play with the mix on juices that I used to buy, using the same flavorings. Nothing I do is that complex. The most complicated I've made uses three flavors. Some have EM, AP, or Vape Wizard to smooth or round out the mix.
At 6 months into DIY I'm still a Newbie, but learning every time I create a batch. I keep my DIY recipe sheets from EjuiceMeUp, but I'm lazy at note taking. I need to do that better. On the plus side, all my bottle labels include the percentages of each ingredient, including Nic, and I'm saving my favorite recipes in EjuiceMeUp.
Like Dannyv45, I like most of my juices better than the retail versions I used to buy.