Πῶς κρινειν；How to choose？

To be a happy man, Aristotle claims that we have to be “active in the activities that conform with virtue.” And, he also points out, “…For our character is determined by our choosing good or evil, not by the opinions we hold…” and “…Also, a choice is praised for being directed to the proper object or for being correctly made…” 

The quotations above suggest that we, as human beings, must be making the RIGHT choice in doing the RIGHT activities which conform with virtue to be happy. But, how?

There are so many things I would like to do/learn in my life, but how can I do all of them before it's too late (i.e.: death, getting old, etc.)? How should I make my choice without regrets? Should I experience all of them and decide which to drop when I meet the threshold? Or, should I focus on one certain thing without finding out which one is "the one"?

Aristotle! You have shown me that making choices deliberately is utterly important in life, but you never tell me the “how”? (At least, I couldn’t get that point reading your “Ethics”).

Oh my δαιμων, could you please help me answering my doubt?