Make sure you do the accommodation tours. It's important to see what the rooms are like
Do the campus tours. We went round Exeter at the beginning of the month and found it beautiful. However, the subject session was rubbish (Ancient History). Only the prospective students could attend those but apparently they all nearly fell asleep because the lecturer waffled on interminably about 20 credits from here, and 30 credits from there....
What they want to hear about is why they should study that subject. Warwick did a brilliant job on Saturday of enthusing the students, talking about the specific areas of interest of the lecturers and what the options were.
Also one uni just said "oh we only look at grades", but another said, "the department looks at all applications, and reads the personal statements, looks at experiences, EPQs etc etc.
Don't rush it. It's important to walk around and absorb the atmosphere.
Do go to any drop-ins in subject areas.
Do look at the buildings your DC would be based in, ie where is the Law / English / Maths centre etc
Be enthusiastic