you don't need to overthink olive oil. but a little knowledge goes a long way. 

if it tastes like nothing, or worse, like the back of a cabinet, maybe use it as motor oil? (please don't actually do that)

good olive oil has life to it. a little bitterness, a fruity nose, a peppery kick at the back of your throat. that's what the good stuff has. 

check the bottle. dark glass exists for a reason — light kills olive oil slowly. a pretty clear bottle on a sunny shelf is basically a countdown clock. forget the "best by" date. look for a harvest date instead. olive oil isn't wine. it doesn't improve with age. the fresher, the better. if there's no harvest date, that's already telling you something. 

and the most important thing ... actually use it! don't save it for a special occasion. pour it on eggs in the morning, finish your pasta with it, dip bread in it while you're standing in the kitchen, or even chocolate (we do it, and we love it). the best way to learn what you like is to make it part of how you eat every day. 

that's it. that's the whole guide. the team at izzi doro hereby knights you as a connoisseur of olive oil.