You can decide in any situation based on one thing: if love/care/compassion increases by doing something, then that is the best decision. You can go back in your life and see that whenever you did that, you were happy later about that decision. Myself, I can say that I always not only felt but can prove that when I took a decision not based on this principle, I took the wrong decision. Also, whenever you take a decision towards your passion, that is always right, since in that you are showing care/love/compassion to yourself. (In turn it increases care around you, too – that is the exponent of your rightness in your decision.) There are many different theories and I will write about them, but in short this is what I have experienced leading me to a good decision.