I had a face to face assessment earlier this year. I feel in retrospect that I was very unprepared for the assessment, though I came away with a diagnosis. One thing I did which was very unhelpful, was to try and interpret the questions day and night before the days itself. This made me very anxious, so I guess what I am saying is try not to over think it, if you can help it. It might be useful to write down some examples of social communication, difficulties, sensory issues etc, both from childhood and currently.
There were multiple questionnaires which switched between childhood and adulthood, so I wished that I had made more notes. I found it easy to answer the questions in short form, but got a bit tied up in knots trying to come up with examples, there and then. The online Aspie Quiz was quite useful, I looked at this after the event and wish that I had found it sooner. I did provide old school reports, as my parents are very elderly and I didn't want to include them in the process. I was not very successful at dropping decades long masking.