Even if you'll get the correct answer for that particular situation, OP, I guarantee that it's not going to be correct in each and every situation. The trick is to always make the right decision. Can you do it all the time? No. Can you do it consistently? Maybe. That's the beauty of soloq. When the skill is somewhat equal, it's all about the mind games. It's a game of whether someone does something brilliant or fucks up massively.
What I do, is train myself to predict the most presumable outcome of each action that I can make right now and I choose the one that I think benefits me the most. It may not help you with deciding whether to follow your teammate or not at first, but it should certainly help you to stop doing stupid stuff like going places for no apparent reason, than walking back and missing out on farm and exp. Your every action in game should be targeted towards a certain goal whether it's a minion wave, gank, or an objective.