If you've been paying attention to your life activities, you've already noticed that there is a general maxim for activities: if it is easy and entertaining now, it will probably be detrimental in the long run, and if it is hard and boring now, it will help you out down the line. Obviously there are exceptions - playing with a pet is easy and fun, yet has documented positive psychological effects, and doing something like fitting a lightbulb in your mouth doesn't sound fun nor is it easy, but that's not going to do much for the future you.
But those are dramatic, and rare exceptions. Scrolling your Facebook newsfeed, watching your favorite television show, tearing apart a fast food burger. These are all easy to do, and are very fun while you are doing them, but once they are done, you don't have much to show for the effort other than those fleeting moments of entertainment.
Meanwhile, think about writing something, about working out, about doing language grammar drills, or choosing to eat healthy. These are things that are classically difficult and often boring - everyone always tells themselves excuses in order to get out of them. However, after those actions are completed, you always have something to show for your time, be it a blog post, toned abs, or a better understanding of how to conjugate things in Portuguese.
There's the Past, Present, and Future, and the things that feel good in the Present look silly and trivial in the Past. The more work you put into the Present, the brighter the Future becomes. Our minds are just hardwired to seek pleasure not pain, even if the pain is just the monotony of forcing yourself to do something without an immediate payoff.
So how can you buck off your brain's whims and choose to do what's important? It's simple - choose to do the activities which will still matter in one year. One year is a long time - long enough to make you forget all the little silly things you did last year, but not so long as to be unimaginable. You could possibly scale this time period down to as low as 3 months, but the point is to have an interval that is long enough to make you forget the things you did in the day. Let's stick with a year for this example.
Do you remember what you did one year ago? Unless you use a life logging program, chances are you do not. But even if you do not remember events down to the exact date and time, I'll wager that there are certain things that remain in your brain from that time. Things like strong emotional memories from friends or family, or perhaps a trip you made somewhere. Regardless, what you will not remember a year down the road is the time you spent the whole day browsing the internet aimlessly.
And if whatever you did a year ago was constructive, you don't even need your fickle memories to remember it - it's still there! If you wrote a piece of writing or made a piece of art, it will still exist in one year and you can go look at it whenever you like. For the non-physical things that require continuous work, like language learning, friendships, or physical fitness, assume that you will continue to pace importance on it between now and a year later. If you lift one weight between now and next year, it won't do much, but if you continue to lift weights every day, then that insignificant action will have repercussions no matter how far down the line you go. The effects stack on top of each other.
So think about this principle the next time you find yourself deciding what to do with your time. Will this matter in a year? In general, it will if: it stacks onto or provides a foundation for further knowledge (study of particular information towards a goal), it contributes to your health (eating healthy, exercising, taking time to play with others), it creates something that will help you later (writing, pieces of art), or it takes you out of your comfort zone (traveling, exposing yourself to new people).
In regards to interaction with others, think the same way, but be a little more lenient. ("Be ruthless with time, and gracious with people"). Is this person/group somebody that I would enjoy seeing in my life a year from now? Are we doing something that has the potential to create a lasting, positive memory that will remain in my brain far in the future?
I say all this because I returned for my final year of college after a year abroad, and noticed that a lot of the people and things that I had spent my time on before I left were no longer people or things I still wanted to do/see. Acquaintances dropped out of view, while my group of core friends remained loyal and important. It really taught me what was important, and which things I did still mattered. Now, I am trying to shape my final year with the above principle in mind - so that even if I left again, when I came back I would be able to build upon what I do now.
(I realize that for many readers of SETT this is hardly revolutionary)