How to perform a total synthesis on paper ? (Think before to make it in lab)
Retrosynthesis, the way to determine which cuts to make and which steps to use in which order (at least in the general picture), is an art. It is not a science or a craft, it is an art. You learn it by doing it and there is only so much you can get taught by others.

Recently, a multi-group seminar I attended started a ‘molecule of the month’ challenge. We were given a molecule and divided into groups. Each group then had about six weeks to come up with a total synthesis plan, find literature precedence or good arguments for all steps and then present it. Our basic strategy was to draw substructures into SciFinder and rely heavily on its reaction search functionality. With more experience and having read more synthetic journal articles, we probably would have known what we would want to go for.

Finally, I feel like adding that sometimes it is not the molecule whose total synthesis you are publishing that piques your interest. There are also those that primarily do method development and then try to find out ‘which molecule could be a good target for the new and super-cool method I just established?’ Thereafter, the synthesis is modelled to fit the desired novel key step. This paragraph is just to show an alternative approach to total synthesis.