As I said, my DD was complicated as she did AS and A at the same time and due to an admin error wasn't cashed in for 1 of them.
From what I recall (and it was frantic- holding on 4 phones at 1 point)
She found a clearing place at a uni she had applied for but rejected as she thought the offer was too high. She got their grades I think but they were very slightly lower in clearing. They couldn't formally offer her a place but held one and we had to keep calling in to keep holding it.
I then got the exam board to cash it in (that was done later Thursday and updated on the UCAS system on Friday I think). At that point she then had an unconditional offer showing from her 1st choice.
We had already spoken to her 1st choice- I got the direct line and name (top tip - do that) of a lovely lady in admin who then released her when I called as soon as it updated. When she got her 1st choice to release her I thought we had done it. Only for it to bounce to her 2nd choice. They were not as helpful.
The 2nd choice initially refused and said they didn't release- then said it could be 5 days. I almost went to the uni (2 hours away) as I was getting nowhere.
Finally at about 8pm on Saturday they agreed to do it. But it didn't update overnight. I called on Sunday and they said they were now only doing updates daily to UCAS (was hourly on Thursday). I was considering who I knew who might know the Vice- Chancellor! when it suddenly came through.
At that point she was straight onto the uni she was holding unofficially and it was done in less than an hour- accommodation booked, deposits paid.
The course tutor from the course that she was trying to get on did call on the Saturday and said that she was on the list and not to worry.
Take lots of notes- write it all down. Try and get the clearing grades before you call and course codes (or rather while holding). Have your GCSE and A level grades/subjects ready- they asked for them.
Start searching the accommodation at the same time- the quicker you accept the place then the quicker you can do the accommodation. For us they just rattled off a list of availability and you have to chose whilst on the phone- so be clear what the preference list is. Luckily we knew the town and roughly what each accommodation was.