No expert, but here's some advice from my own experience.
When you get to the court on the day of your hearing, find the usher and give your name and details. Tell them it's your first time in court and ask exactly where you should go and what you should do; they are usually pretty helpful. The next thing to ask is to see the duty solicitor; he/she will answer any questions you have and will represent you in court free of charge. This will help make things a lot less stressful for you. It's really not worth paying for your own solicitor if you are going to plead guilty. Obviously dress reasonably smartly and be polite (you address the magistrate as "your worship"). You can ask the duty solicitor to apologise to the court for you and express your regret for your behaviour, which never does any harm. It will help if you co-operated with the police at the time of your arrest, and also if you plead guilty. Be prepared for a long day waiting round in the court building; the more complex and "important" cases are usually dealt with first, so you might end up last on the list. Not good for the nerves!
You will get a minimum 12 month ban and a fine. Was the reading of 84 for a breath test or a blood test? If for a blood test you were only just over the limit, but if for a breath test it will push you up to the next category and a minimum 18 month ban. (See the sentencing guidelines on this website.) The amount you are fined will depend on your income.You will usually be offered a rehabilitation course which costs about £130 but will take up to a quarter of the time off your ban (eg up to three months off a 12 month ban). Remember that the ban comes into effect immediately (so don't drive to court because you won't be able to drive home).
Appearing in court is scary and unpleasant but it probably won't be as bad as you think. And you won't go to prison!
Good luck; let us know how you get on.
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