First of all, please, please don't go alone. You need a family member or friend present to make sure you get a fair hearing and to prompt you where appropriate. It's never a good idea to attend these things without a witness to what goes on.
Secondly, hopefully you have kept a copy of your application form, so study it properly and make sure you are clear on what you have written because your assessment will be based on what you have said. It's very important to remember that anything you put on the form which is not discussed at the assessment will not be counted towards the points scored - so if, for example, you need a particular type of help and you have detailed it on the form, but you subsequently forget to mention it at the assessment, it will not appear in your condition history on the assessment report, and will not be considered by the decision maker. So make sure you tell the assessor absolutely everything, no matter how embarrassing you find it - I guarantee you won't be telling them anything they haven't heard before.
You will be watched from the minute you get in to the minute you leave - this is called informal observation, and the assessor does this to identify any behaviour or movement inconsistent with what you are reporting about the effects of your disability.
The assessment will start with your condition history and any medication you take, then the assessor will ask you to describe our typical day. The assessment then goes on to assess the specific activities in the daily care and mobility categories.
It's also worth remembering that the distance between the waiting room and the assessors room will measure at least twenty metres, so if you can walk it seemingly with no problems, then you will not qualify for the enhanced rate of the mobility component.
For each activity, the law says you must be able to complete that activity safely, in a timely manner (less than twice the normal time taken by a non disabled person) without undue pain or discomfort, and to an acceptable standard, so if you have difficulty with any of the things assessed it's vital that you tell the assessor what it is and why. Also, assessors are fond of suggesting aids and appliances because these score lower points than having help from another person, so if you cannot use a particular aid, say what it is and why you can't use it. Similarly, if you have an aid and still require help, say so and say why. A very important point particularly for yourself, if you are short in stature, is the cooking test. The law says that the actual cooking of a simple meal should be carried out at waist height, using a conventional hob or microwave - the use of a conventional oven is discounted. The preparation - peeling, chopping etc, can be done lower down, at a table for example, but the cooking is specific to waist height. I would imagine the only way you could achieve this is with a high perching stool, but since you are short in stature you would probably need help to get on and off one, and there would be a serious health and safety issue, since your feet would probably not touch the floor even with the stool on its' lowest setting. All of this needs to be brought to the attention of the assessor.
Finally, the legislation says that there is no time limit on the assessment - each case is different and the time taken will vary. In practice assessors are limited to 45 minutes. Make absolutely sure you are not being rushed and if the assessor attempts to cut short your answers, insist you be allowed to finish your point. This might sound difficult, but oh need to make sure the assessor understands your difficulties and they cannot do this unless you explain them in full. Also, at the end of the interview, the assessor is supposed to go over their answers with you to make sure you agree with what they have written. In practice, a lot don't, and since not all claimants are aware that this is their right, they are usually not challenged. Ask to see what is written and make it clear you know this to be your right. The alternative is an assessment that may not accurately reflect what you have said, and that will lead to an inappropriate award, which you will then have to challenge. If there is anything else you want to ask before your assessment, please do and I'll help if I can.