First of all, grades. It decides everything, the school you can choose, the city you can study in and of cause the major. I didn’t try hard on studying, so my choices are limited.
Then, my interest. Actually I am not a big fan of biology, but it’s much better than physics ( because I am really suck in physics). I am good at maths, but I like something more relative to daily life. It’s a little ironic that I study chemotherapy of breast cancer as my subject of graduation, that’s not daily at all.
The last, jobs I can find in the future. I really didn’t looked up carefully at first, so now I am trying to gain a master degree to postpone the job finding issue.
And also, I think it is important to know what lessons you will have before choosing the major. I am not afraid of doing any experiments, but the screaming that I suffered in every animal experiments for four years makes this advice’s point.