Let me offer you a suggestion or two or more....
First pick a niche, preferably one you already know. Then find the top three sites and then find 3 ranking around 35th place.
Now compare the sites and analyze them. See what the three sites ranking 35th and lower are not doing as compared to the sites in the top three spots. It will very soon start to become obvious as to what is not being done.
The is a caveat though... you need some tools.
Start with Screaming Frog and Web Me Up.
Now read all the threads on this site and try to soak up the info in them.
Now go create your own site and rank it. Unless you can intern with a working professional, trial and error are your best options.