Do you have any subjects that you prefer? If so you could research careers linked to those subjects.
After you find a couple you like, pinpoint the countries/unis you'd like to go to- something must have popped up in your mind- and look for the suitable course that falls in line with your subjects/career option.
I would also suggest interning at a couple of places related to the careers you chose earlier. This might help you choose as you will be able to experience and decide which options you prefer.
Hope this helps! :]
I would first figure what you will need to live: Take the amount that a flat will cost you, what you will need for groceries & eating out, how much you will need for clothing and transportation. Ask your 'rents or your mate's 'rents what it costs them. Many ppl won't have a clue, but some should know. I would recommend NOT figuring on a 'room-mate'. Those arrangements often don't work out, and you could end up not being able to afford a place [i.e. homeless], or having to put up with a very undesirable situation. If you can find a compatible room-mate, so much the better - it's money in the bank.
Then consider which careers in the STEM area would appeal to you. Perhaps computer programming [of which there are hundreds of thousands of different jobs]. Engineering might be an alternative too. Contact the professional societies [like the IEEE for engineers], and ask them to put you in contact with degreed professionals that would be willing to talk to you about their profession. Tell them that you are considering a career ..whatever it is. Ask them to refer you to people who have been working in their field for at least 10 years. You don't want fresh graduates - they don't know how things work yet.
The first two years or so, for most STEM degrees are pretty much the same - so if you decide to change from Computer Science to Electrical Engineering, nearly all the courses will be the same. Make up a list of questions to ask your degreed professional. Things such as: "How much do you make, where do you see yourself in 5 yrs, 10 yrs, If you had your education to do over, what would you change, What other careers did you consider, Why did you decide against them, If you had to find another job - how difficult do you think it would be, and how long would it take, Have you ever worked overseas, where, did you enjoy it, where else have you lived. This should give you a few ideas as to what to ask. WRITE DOWN the questions - so that you ask the same questions of each person you are interviewing. Also, write down the answers. Take them home and consider them. Interview the people one at a time. You want an individual answer, not a 'committee' answer, and you do NOT want the interviewees 'intimidating' each other. They will probably be much more honest and open if they are dealing only with you. Be SURE to thank your interviewee for spending time with you. After you go over their answers in your notes, send them a written 'thank you' to back up your verbal thanks - by mail if you have their mail addy - or by email if you don't.
Best of luck!!!