For DS1 we went to the July open days, those that didn't clash, and also some in September. They are usually arranged in outside of uni term time. We had to book to get on many of them, you couldn't just turn up.
I'm not sure what to do for DS2 because I won't be looking at Russell Group universities this time!
So we'll be starting from scratch. Also, I think that maybe a higher apprenticeship might be more useful, so I'll have to investigate those as well.
By the end of Y12 DS1 was set in what degree he wanted to do. A few months of A levels had enabled him to know better where his strengths and weaknesses lay. He needed STEP (Cambridge maths entrance exam) to get a good offer from his universities of choice, whilst having ruled Oxbridge out early on.
Have a look at some universities' websites, their entrance requirements are pretty easy to establish. It's too early to have a good feel of what grade our DC are likely to obtain. The step up can be a big shock to even 12 A* and A grade GCSE students.