Consistency is key. Make sure you meet God daily in prayer and get accustomed to recognizing His “still, small voice” (see 1 Kings 19:11-13).
Meet God in the Sacraments
You will only know His will if you are filled with the grace He gives you in the sacraments – most notably, frequent confession (I recommend at least monthly) and Mass (ideally more than once a week).
Imagine yourself in the various vocations and get excited about what the Lord can do in you and through you in each of them. [Bonus points if, beyond your daydreaming, you get out and ask your parish priest if you can shadow him in some of his priestly duties like sick calls or sacramental ministry so that you can have experiences to inform your daydreams!]
Clean Your Room
You can’t find something you need in a mess. It’ll be hard to find your vocation if your life has no order to it. So, try to build up an essential structure for your days and weeks: When are you going to pray, serve, study, exercise, sleep, etc.? Also, literally, clean your room; order in your room can often help to develop order in your soul.