I do not pretend to be an expert, this is just what happened to me.
The court is on 3rd avenue in Pioneer Square. This is a very bad neighborhood. The block that the court is on is heavily patrolled by security and police, but around that it's half-naked screaming homeless guys, drug dealers and prostitutes as far as the eye can see. So, be careful.
Take the bus if you can, but if you want to park, do not pay more than $13 for the day.
Prepare for your jury duty the same way you would for a trip through airport security because, guess what, you're going to have to go through airport security. You can bring liquids (And if you want coffee bring some, the free stuff is terrible) and you won't have to take off your shoes. Don't wear a metal belt buckle or have anything in your pockets that you don't want other people to see. Also, no knives or other weapons. Duh, but yeah.
The size of the security line varies at different times of day, so always plan on having to wait in line to get through security. The longest I waited was 10 minutes.
The jury room is on the first floor. After you go through the metal detector, head straight back through the elevator bay. There's a sign pointing to the jury room door. Open that door. Give the lady at the counter the badge that came with your summons in the mail and she'll read the bar code with her scanner.
You have to do this to check in. If you don't check in, you don't get credit for being there.
On the first day, you have to be there by 8AM. After you arrive, you pick up a plastic case for your badge and a bio form. Grab a pen and find a good seat. Fill it out after you sit down. It asks things like have you ever served on a jury and have you ever been party to a lawsuit. It also asks your age, occupation and how many kids you have. Be prepared with the info because they can charge you with perjury if you lie.
Choose your seat carefully. There are three basic areas. There is an enclosed room set up like an office for people with laptops, the big room and the rows of chairs.
Don't sit in the rows of chairs unless you want to feel like you're on a bus for an entire day. The office has limited space, but if you get their early and have your laptop, it's great. I opted for the big room. Get a seat near an outlet if you want to charge any electronics. (There is free wifi while you're there, but don't depend on it. It fades in and out. I would approach it with the attitude of just being happy if it works. If it doesn't, ask once then let it go. Otherwise, you'll go nuts.)
After you sit down, they show you a video and a judge talks to you about how important being on a jury is. All of this makes it sound like you don't have to be there and you chose to go anyway. This is not the case. Really, they just don't want a room full of angry people so you're constantly being thanked and reminded how important it is that you are there protecting democracy and justice. Or something.
My group was pretty easy going, but from the way the women in charge talked, it can get bad sometimes. The staff is very professional and friendly. If you have a question, ask. I saw them bend the rules in sensible ways to make people happy and in general make decisions that made the day more pleasant. They are also happy to recommend lunch spots, coffee shops and know the closest store that sells what you need.
There is a podium at the head of the room and as requests for juries come from judges, they will be read from the podium. There are speakers everywhere, including the bathroom, so don't worry, you'll know when your name is called. You will be given a number that you have to write on your bio form. You will then trade your bio form for a big laminated version of your number.
These numbers are important. The lower the number the more likely it is that you will be on the actual jury. If they reach the required number of jurists before they get to you, you are released back into the jury room.
There are pop and snack machines in the jury room, including bottled water. They have a filtered tap water dispenser as well, so bring your own bottle if you want.
They'll give you at least an hour for lunch, but on one day they gave us 2 an 1/2 hours. I went to lunch at Salumi on that day. It's a wonderful salami shop that makes the most delicious sandwiches. Unfortunately, there is always a line. If you go, get the Muffo and be prepared to wait 20 minutes for lunch.
I also discovered that Elliot Bay Books will give you a 20% discount if you flash your jury badge. (Which you kind of have to. You're required to wear it the entire time you're out for lunch.)
The second day you can sleep in and get there at 8:45 AM. Be forewarned that this is the worst time for security, long lines.
Truthfully, being there is like waiting in an airport for a plane that never comes. Bring books, games or whatever you use to fill time.
I found the experience exhausting. Constantly waiting to see how you will be required to spend your time. Getting on a jury means that you could be forced to go there for weeks. Each time she went to the mike to read her random list, I had my own private panic attack.
Good luck! Leave any experience, corrections or advice in comments so that other people can benefit from your genius.