I'm a year 12 (going into year 13) student researching unis too!
What you want to be looking at depends on what's important to you.
A couple of things I'd suggest looking at are:
-The quality/prestige of the University: You can look this up on league tables and university ranking sites, they don't all say the same things but attending one that's fairly high ranked has all sorts of benefits for employment etc.
-Courses: Make sure to look up all the modules included in your course, you might like the look of the university, but if the course modules at that uni are boring then you might find it less enjoyable and possibly more difficult.
-Requirements: Make sure you meet all the requirements for your courses. For example, some courses require you to have certain GCSEs and they don't always make this too obvious so sometimes it can be easy to miss!
-Accommodation: You're going to be spending the next four years at the place, so you want to make sure it's somewhere nice! One of the best ways to check whether or not you'll like the accommodation is to attend open days.
-Location: Whereabouts do you want to go? Location can make or break a university, with some universities being in the center of city life and others being in quaint countryside villages.