it's all about experience and introspection.. you have to be brave enough to try things.
i went travelling for a year and still do whenever i can, i've tried almost every low-wage job under the sun (fundraising, fruit picking, social care, catering, etc.), and at uni i do as many societies as possible. it's all about that experience- i would say at least 3/4 of the things i try don't work out, but because i try so many things, i've got so much more variety in my experiences than other people, and sometimes finding out you don't like a certain thing allows you to make choices that much more easily. when i was 18/19 i made my mind up that my early 20s would be all about experiences, because once i got to the stage where i would be making life choices i wanted a solid foundation, a detailed picture, from which to base those decisions.
now if i want to think "what are my strengths and weaknesses?", "what makes me happy?"- i can plan my life out so much more easily. it's also about not being restricted by comfort zones- i've never been naturally adventurous, but i've pushed myself to attack anything that i feel uncomfortable about, so that my choices are not restricted. if you never do that then who knows, maybe there is a certain life path that would make you happy, but because it seems so out-there to you it ends up being something you don't consider. for example, i'll probably have kayaking as a hobby that stays with me, and i try every adventure sport i can these days, but there was a time when the idea of me doing something things like that seemed well out of character.
just, in terms of the experiences you already have, figure out which ones make you happy and which have made you unhappy and try to incorporate that in your career plans. at the same time, if you're going to uni you still have a few "non-responsibility" years left, so use them to gain experiences you normally wouldn't do.