Hello chaps, new to the forum. I'm a qualified driver of a few years so going through the assessment stages is still fresh in my mind and I will offer advice where I can.
The TOC I did my assessments with was conducted over 2 days. I passed stage 1 and then approximately a month later undertook and passed stage 2.
I had a face to face interview on the stage 2 assessment day. It was conducted at the end of the day after completing and passing all the various tests. Note this is separate from the management interview which will come at another date assuming you pass stage 2. I found the stage 2 assessment day mentally draining but had prepared for the interview in advance in case I did pass the various tests and it paid off for me. Of the 5 of us that made it to the interview stage I was scheduled to be interviewed last so had a bit more time to compose myself but would have probably liked to have got it out the way early.
In terms of preparing for the various tests, I'm not sure you can. What helped for me was that I had a very clear idea of the kind of tests I would be taking, based on the material that was sent through the post to me before. So on the 2 days nothing took me by surprise and this relaxed my state of mind. I suppose the only test you can practically prepare for is the Group Bourden one by downloading the tool.
A cliché I know, but the most important thing for me is to remain calm and focused when you do the assessments. Easy for me to say but so very important.