Given the numbers of people applying compared to the number of slots available, every stage until you graduate IOT is an assessment stage.
Assume that you are being watched and assessed at every stage. I applied through the SCLO at uni, but I still went to all the AFCO briefings and did the whole jacket and tie job on the assumption that any paperwork with my name on it would end up at the same place.....OASC
Keep up to date with current affairs and military issues in general. Good things to get your head into include:
Quality newspapers
Guardian / Observer
Economist
Time
Newsweek
BBC website
Reuters website
CNN
Good bits to concentrate on are the front page articles, international pages and the editorials which give opinions and points of view on various issues. Regardless of what the headlines say, the boards will be interested in what you think ....... we have enough 'Yes Men' in the RAF, we don't need anymore.
As for the dress issue, shirt and tie every time. At my OASC board back in the distant past, one guy pitched up in black trainers and leather jacket. Didn't see him again after 4pm on the first day. Assume every stage is a job interview and you wont go far wrong.
Finally, don't worry too much. Officers (and SNCO aircrew) aren't superheros and the boards are all human. They will know you are nervous and take account. Prepare in advance, otherwise expect to fail; importantly, be yourself - the selection boards have highly tuned crap detectors- they want to see the real you, not what you think they want to see. Most of all, relax and enjoy it, you'll do so much better ....... took me several years and 2 attempts to work that one out!
Good luck!!