Updated: May 19
The question shouldn't be about "how do I give less fucks," instead, if you find yourself giving "fucks" about stuff you know you actually shouldn't give a fuck about, it should signal to you that you have a surplus of "fucks" to give. Therefore, to "give less fucks," one shouldn't stop caring in general (that's called depression); instead, he/she should discover what brings that person a sense of fulfillment. So stop redirecting your focus towards useless things; work on your passions, and find stuff you care about. This way, your "fucks" will be directed towards something you care about - your "fucks" are precious, good "fuck"-management can make you a very successful person, don't waste them on low-value or pointless activities or things or people.
Take this with a grain of salt. This message refers primarily to people who feel like they overthink or care too much about little things they know they really shouldn't. If you have time to overthink, you're not managing your time correctly.