Re: Being ready
For the lower kyu grades you can pretty much decide on who will pass just by watching them step on the mat.
This is not meant to put anybody down, but if you have put enough effort into your training it will show, and the way you handle yourself in a dojo will speak volumes about you level of aikido.. and let's face it. The first couple of gradings are more about showing basic understanding of the whole concept of practicing aikido.. gradually growing into an ever larger display of technical proficiency (in lack of a better word) as you go through the kyu grades.
From shodan and up it is still about technical ability but other issues become part of the evaluation as well - and these wary a lot within different styles. As somebody said above.. just enjoy it - and don't spend too much time thinking about it. It is just one of a million steps in your aikido.
Have fun (also when grading)