This is kind of intangible advice, but... intuition. I go with what feels right at a given time. That's not to say I'm fickle or don't plan ahead, but being aware of my desires in the moment, thinking about how things feel to me, and trusting my gut feelings goes a long way. Don't go by stereotypes or external expectations, narratives, or structures. Do you. Don't worry about looking or being cool, focus on looking and feeling a way that feels right for you.
Practice reflection. Keep a journal. Find a counselor. Ask yourself what you want and write and think on it.
This sounds a little more like a /docta/ thread, but since this is /fitfa/, I'll talk a bit in fitness and fashion terms:
Fitness: don't worry about what body type or build *chan fitness boards tell you is the best or girls like the most or whatever the fuck. Take a realistic look at yourself, think about how you will feel most comfortable in your body, the look that will make you feel really proud of yourself and your accomplishment and discipline. Work out. Try different things. Lift, do yoga, run, bike, swim... find what leaves you feeling really good and what feels like the most fun (or the most enjoyably unfun, if that's what you're looking for) and do more of that. Maybe you want to be super jacked, maybe you want to be lanky and flexible, maybe you just want to look like a pretty normal but very fit regular guy. Think about it.
Fashion: again, ignore what imageboards say as far as specifically how you should dress. Accept advice, sure; seek feedback, sure; look for tips and inspiration. But take everything with a grain of salt and at the end of the day, do you. Do what feels comfortable for you. Think about what you value. For me, I've been finding more and more that I value minimalism and high quality. I don't want to buy cheap made-in-china shit, and I don't want heaps of clothes spilling out. I want a few versatile key pieces, nothing too flashy, just a handful of items that I can mix and match. I've started to realize that I don't really want to make a big statement with my clothes, I like to play it low-key. You may be different. You may enjoy flashiness. You may want a more extensive wardrobe. That's cool.
Think about what you want, cultivate habits of self-reflection, learn what it is you value, and build your goals around that. And above all, be willing to change. Your goals should not (and probably cannot) be set in absolute stone. As you grow and change, so will your needs and desires. Be willing to let them morph and take on new shapes. Be willing to go through phases. Be willing to grow, shift, and re-evaluate.