Seneca describes the problem - we are wasting our most precious resource: time.
pay close heed to the problem, you will find that the largest portion of our life passes while we are doing ill, a goodly share while we are doing nothing, and the whole while we are doing that which is not to the purpose.Regarding how precious this resource is:
What fools these mortals be! They allow the cheapest and most useless things, which can easily be replaced, to be charged in the reckoning, after they have acquired them; but they never regard themselves as in debt when they have received some of that precious commodity, – time! And yet time is the one loan which even a grateful recipient cannot repay.What are we to do? What if most of our life has already past? What do we do now?
I do not regard a man as poor, if the little which remains is enough for him. I advise you, however, to keep what is really yours; and you cannot begin too early.The answer is, we have enough time, now. We must seize the day and make the most of the time while we have it.
What else can you do, to ensure you don't waste your time?
What I've learned from any others is that planning is big. Plan your day, set goals and establish systems to live your life by. If you are aimless, then the first task at hand is to aim. Find out what you want in life - what you want to be, where you want to go and live, what do you want to do. Make a plan to acquire real, usable skills which will enable you to earn a living. Be sure the skills you learn are sustainable and that they are something others are willing to pay you for.
This establishes "a base" for you. This gets you up and working and contributing to society. This also buys you more time to work on higher value activities. Also know, that very little is needed to get you 'up and working' as it were. Thoreau's Walden proves this - read it if you must. In today's post-modern society, any person with a healthy body and brain can make a living if they manage their wants and desires.
Once your base is established, work to grow it and try to find ways to be more efficient at it. All the while, you should be finding and understanding your unique, core values - what makes you happy and what your unique contribution to society is or will be.
And always be sure to set aside time, every day, to work on understanding your philosophy and to live it. Read Marcus Aurelius, Seneca, Epictetus and other philosophers. Think about it, talk about it, embody it.