I’m not a Slytherin at heart, but I do know a few and getting into their heads has been a bit tricky. One of the more important Slytherin questions for non-Slytherins (esp. Hufflepuffs) that I eventually extracted out of their heads is the following:
“How do I do this thing I want to do AND benefit myself in the future?”
Many people act selflessly in their actions while attempting to care for others or take actions purely for temporary gain and fun while not considering their own upcoming futures. Just because your current actions weren’t chosen or designed to benefit your own future, that doesn’t mean they can’t be slightly modified so that you gain power, status, wealth, or other value in the future as well.
Whatever you personally value (knowledge, love, pleasure, kindness, wealth, etc.) you can often turn that into opportunities to gain other possible benefits later on. You can choose to do an activity with a friend instead of alone, choose to do the action while observed or with a wider audience and number of people affected by it, or you can ensure that the action builds a skill that could actually be useful to you in the future.
I don’t suggest that you stop doing whatever it is that you want to do. By all means, keep doing whatever it is that you want! I merely suggest that you might alter things ever so slightly so that you gain even more benefit later on down the line.
This way you end up both getting what you want right now and being more able to get more of it in the future. You could get more knowledge, more kindness to people, more love towards you, and many other things. There may not always be an easy or readily available answer to the question of “How do I accomplish this task while also benefiting my future self?” but I bet there’s an answer there far more often than you imagine.