Hey Timothy, there are a lot of things you could do that I think would be really valuable!

• Participate in the virtual Stanford Existential Risks Conference on February 26 and 27. Apply by February 22 – it only takes about 3 minutes to apply.
• Participate in a virtual program by EA Virtual Programs. A program involves about 2–3 hours of time commitment per week for eight weeks. I might recommend starting off with the Introductory EA Program (and if you have time, also the Precipice Reading Group), and then the In-Depth EA Program. After you've participated in a program, you can start facilitating for it, which is really helpful for having people more engaged with EA!
• EA Cambridge is currently running virtual AGI Safety Fundamentals Program, among other programs, but applications are now closed. You can register interest and get notified when these programs re-open in the future.
• Apply for an EAGx conference near you.
• Apply for career advising from 80,000 Hours. Highly recommended if you think analytically about how to maximize the impact of your career and are open to working on addressing top longtermist problems (e.g., AI safety, biosecurity, global priorities research). Besides providing advice for what career paths to consider, they also try their best to connect you with other EAs working in relevant areas.
• Apply to facilitate for LEAF in Oxford, UK for 1–4 weeks in August. LEAF is "a Summer programme introducing intelligent and altruistically motivated 16-18 year olds to ideas about how they can contribute to tackling some of the world’s most pressing problems, especially those that might have lasting effects on the long-term future." Applications to facilitate are due on February 27. See Jamie Harris's post about this in Effective Altruism Job Postings.
• Apply to the CERI Summer Research Fellowship and Swiss Existential Risk Initiative Summer Research Fellowship
• Apply for a summer internship at the Global Challenges Project in Berkeley, California. Applications are due on March 13. I'm not sure if the application form is public but you can shoot them an email if you'd be interested.
• Apply to the Happier Lives Institute Summer Research Fellowship (deadline 20th March). "The fellowship provides an opportunity for students and recent graduates to gain hands-on research experience and receive personal mentoring from HLI's research team. Fellows will be paid $500 a week ($3,500 in total) for the seven-week fellowship period. The fellowship is fully remote and you can choose your own work hours (outside of scheduled calls). Applications close on Sunday, March 20."
• Apply for an (unpaid) internship at Training for Good.
• Apply to other internships listed on the EA Internships Board.
• If the university you're going to doesn't already have an EA group, consider starting a group through the University Group Accelerator Program or advertising the virtual Intro EA Program. I used to think it would be super hard for me to start an EA group, but I think it's quite doable if you have enough free time to run or advertise an intro fellowship. Feel free to reach out to me if you have questions about this.
• I think self-studying would also be highly valuable. For example, if you're interested in working in AI safety, then studying machine learning (especially reinforcement learning and natural language processing). I'm happy to provide some recommendations here.
• You can also apply to general non-EA internships for the purpose of building experience.

Some obvious advice (YMMV) - roughly in order of importance:

1. Improve your long-term physical and mental health- that's often harder later in life and probably the most important thing.
2. Improve your English: English is really important- learning languages is often harder when older.
   1. Ideally, you'd do language immersion in an English-speaking country to increase your functional fluency
   2. Reduce your accent because that's really hard later in life.
   3. Vocab and grammar: Start a Remnote and add vocab that you come across and don't know (maybe also have a look at English anki decks).
3. Do a (research) internship. Universities train everyone to become a researcher, and there are reasons for that, one is that the scientific method is really important to internalize and then also that if you have the knacks to become a researcher that would be really valuable and also research skills are pretty broadly useful, so it might be good to explore this early, but of course you don't need to become a researcher. 
4. Improve your writing: it's a very generalizable and very important skill - you need in almost any profession. 'Writing is thinking'. Take "Writing in the sciences" MOOC. Start a journal and a blog.
5. Get a headstart: Read "How to win at College" (also "Deep Work" and "Digital Minimalism" by that author). There are some studies showing that having more education or being older before going to university increases educational attainment later.

So one thing might be to move to Dublin (you don't need a visa) for a research internship (you could just email Professors and ask for an internship or ask the EA Dublin people there for help). Then do some self-study, go to the gym, socialize on the side.

Some other ideas:

1. Learn to code: this will be very important for almost any research or engineering career, take an intro computer science course or do a bootcamp.
2. Money: The best investment advice is to invest in yourself, so you set earn more money later (e.g. learning, getting good grades, applying for scholarships - which has very high ROI (often >$100/h, but is also good for your CV). If you need to get a job, find one where you learn as much as possible... e.g. tutoring in your subject might not pay as much in terms of $/h, but you solidify/deepen the knowledge of your subject at the same time, and that'll pay off later.
3. If you're atheist consider exploring some sort of spiritual practise like meditation (e.g. with the Waking Up app).
4. If you haven't yet, learn an instrument - also harder later in life.
5. Explore different subjects / become well-rounded: In Europe, you can't take courses from outside of your field of study like. So maybe read some other books - Kagan "Normative Ethics", Polya's "How to solve it",  Sowell's "Basic Economics". Schwanitz 'Bildung',  More textbooks). 
6. Start a project (e.g. social media channel, start a shopify and sell anything).

But note that you could also just go on an adventure like interrailing or something... in the explore/exploit tradeoff when you're young it's good to try a bunch of things.

What do you mean by "regular job"? What's your current job?

If you're able to get a job that's quite different from what you're currently doing, that could be really useful! You can learn a lot from some jobs, and getting paid at the same time is pretty great. On the other hand, you might learn more from an unpaid internship. It might be worth applying to both and seeing what your options are!

I'd definitely prioritize having enough money that you're not in danger of going totally broke if you had to take a couple weeks off of work, and having at least one day a week to just chill.

Edit: I meant you might learn more from an unpaid internship.