Are you going to the Sheriff Court or the High Court?
I've done jury duty twice at Glasgow Sheriff Court.
It really is quite relaxed - the Clerk of Court will talk you through what happens and keep you right. There will be about 30-40 of you, he will do a roll call of who has truned up (many people don't! ) and will give a rough description of the case about to be heard. He will also give the names of the defendents, so that you can excuse yourself if you know them. He'll then draw 15 names from a bowl and you go forward in to the Jury Box (15 in Scotland, not 12).
The Sheriff then swears you in - you can choose not to swear to God - but be aware, if you choose to "affirm" as opposed to swear to God, then you have to take the oath individually (The "God" Swearers" get to do it en masse) (Guess who got caught out? )
The listening to the case really is very straightforward - but be ready for lots of waiting about - both if you are called on to a Jury (legal arguments etc, where you get sent back in to thr Jury Room) and also while waiting for a case to be called. Previous ones can over-run, there may be further legal disucssions before they even call a Jury.
Half the time, the case gets plead out before you even get to make a decision.
Don't worry - if you are called, just listen to the facts as presented, take notes (it's amazing how many people don't) and be prepared to be surprised: often a case may appear to be obvious and then as it unfolds, you realise that while the defendent may well be guilty of something, it either isn't what (s)he is up for, or the evidence that is being presented, despite initial appearances, doesn't actually stack up "beyond reasonable doubt".
For me, it was a real eye opener about how the "other" half lives. But then, I've lived a very sheltered life!