My worthless advice is to get to know as many flavors as you can. Single flavor mixes and then combine them with the other flavors you like or think that you might like. There are times I will taste a commercial juice and will know exactly which fruit flavor they are using just because I am so into certain fruits and some are very distinct. There is no substitute for knowing your flavors. Take notes if you need to.
Some commercial juice companies are the masters of deception when it comes to their flavor descriptions. The art of persuasion can trick your mind to taste things differently. For instance a juice description may say " a gentle touch of white grape" in reality they might get the taste effect from pear and a tiny amount of lychee. Don’t trust the juice company’s descriptions.
Sometimes things are not as they seem. This ties into both of the above points. Know your flavors and try to keep a completely open mind devoid of preconceived ideas of what the flavors are. A good example is vanilla. If you are sure its in there, it could come from so many different flavorings. A straight vanilla, a custard, marshmallows, creams, whipped creams etc. Another example is a juice a local store makes. The description says caramel, but its really toasted marshmallow that when blended with the other flavors such as butter, gives a kind of caramel taste.
Layering. Something I learned about on this forum and you can search for. Once you know your flavorings you will know that its brand A peanut butter you are tasting and know that its the dominant flavor and its never mixed above 7%. The second strongest flavor is brand C or brand B maple or a combination, but you have to test them both and at varying percentages until you get the majority of the taste you are looking for.
Additives. This sweetener, that sweetener, this sweetener AND those other two? Vape Wizard? Sour Wizard? Oba Oba? What do you personally consider an additive? For me, anything like a custard, cream, milk or whipped cream is an additive because they aren’t really my thing but they sometimes have a usefulness in small percentages. Any flavor can be an additive at a certain point. Sometimes 0.25 percent is that underlying mystery flavor your clone was lacking.
Perseverance and patience. You must have both to attempt cloning. Even if you are really good and have some kind of natural talent, you will make plenty of batches that just aren’t right. A friend that has mixed way longer than me has nailed a few clones, but most are just kinda close and he has probably tossed thousands of rejects. Another friend was able to make a really good clone of an older juice. It was his experience mostly, but also because he did detective work and found which flavorings were available at the time and was able to eliminate anything more recent. He also talked to someone that had worked at the company and hinted at which flavors he should try. The last piece of the puzzle is that he found out the owner would only deal with flavoring companies that were close so that he could easily drive for supplies if needed. That cut the brand of flavor suppliers down to two.
So that is my worthless rambling advice. Take it for what its worth, with a grain of salt, with a full glass of water and two aspirin, or just kick me in the nuts in the morning. Best of luck and let us know what kind of results you get.