Here's my advice
1. Pull up the league table for your subject, look at the first 40 or so. Eliminate ones you immediately know you can't get into, now if your pool is too small go deeper down the league tables. From this point onwards, you will not look at the league tables once. All they are is a conveniently ordered list of unis which offer your course, it's quite a poor indicator of actual reputation.
2. Make a list of all of the unis here, and write their grade offers down. You're probably looking for 2 aspirational applications, 2 comfortable applications, and one which can go into either category depending on what unis you end up liking. Don't bother with a safety, low tier unis usually have clearing spaces anyway.
3. Narrow down the list until it's practical to visit open days for all of them. Cut ones based on whether you want a city centre campus or one that's on the outskirts, if it's important that everything's on campus then cut those for which that doesn't apply, ones which do unacceptably poorly in student satisfaction surveys, etc. Now also look at the courses, and make sure they have everything you want in them (doesn't have to be that in depth research yet, for instance in aerospace engineering I cut ones which didn't have much in the way of astronautical engineering modules).
4. You should now be prepared to visit open days. Enjoy yourself!
5. You've visited the open days, now it's time to decide once and for all where you're applying. Take out the ones you hated at the open day, and set aside the ones you loved and you know you're going to apply to. Now it's time for a tournament arc for the remaining places.
6. Draw up a bracket, compare each of the universities with a similar grade offer, and find your favourite by process of elimination. Compare things like the courses, now's your time to read the module descriptions and everything to find out which is your favourite, as well as accommodation costs, general cost of living for the area, campus vibe, etc.
7. If all went to plan, you should now have 5 universities you want to apply to. Now all that's left is to be predicted significantly lower than you expected by your ******** teachers, and then proceed to cry yourself to sleep as all the hard work went in the bin.
I know it's a wall of text, but hey you're the one who asked a very open and complicated question lol