Awesome for you. The retrospective can be one of the most fun and informative "ceremonies" of agile.
So once you get the book, Diana is going to recommended never falling into a rut and tailoring your retros based on what is the needed to be focused on, or to take the team into a new direction.
When you first get started though, simple is very good.
Retrospective Circle - Brain Storm
On a white board draw a huge circle (3-4 feet across) and segment it into three sections. Label the sections "Less of", "Same As", "More of".
Give everyone a stack of postits and sharpies (Don't use ball point pens, too hard to read). Have them start filling them out and putting them up on the wall. (Advanced tip- If you have a lot of team members who tend to be quiet and not talk a lot in meetings, give them a heads up you'll be doing this and give them postits ahead of time so they can generate content before the meeting). EDIT- Highly recommended you have a couple of starter post-its. If no one looks like they are moving to put stuff on the board, put yours up.
Affinity map the postits. If four people all post about the build server, group the postits together. Do this as people are putting content up.
When done, give everyone 3-5 stickers. Explain Dot Voting to them. Make sure they know they can vote more than once for something.
When the voting is done, look for the two to three things with the most dots, no matter the category. If any of these are outside the teams control, capture these to the side and grab another item that the team can control. You want 2-3 items the team can control.
Make a plan with the team right there and then. Who, Does What, By When. Set dates, assign owners. Don't leave the meeting until a plan is in place.
Making it Stick - Action Planning
Now comes the hard part. If you want people to keep doing retrospectives, they need to see value out of it. If they come to retros and nothing ever happens, they will start to question why.
Make sure those items the team picked get planned and acted on. Putting them on big pieces of paper and posting them next to the task board, so they are seen during every stand up is a great way to keep it fresh.
You can completely keep this inside of an hour. My personal mantra is you can do anything you did in 60 minutes in 45-50 minutes.
Meeting Start and Agenda: 5 minutes
Start 5 minutes after even if people are late, Agenda is posted on wall so late people know what it is. Agenda is time boxing the three phases "Brain Storm", "Dot Voting", "Action Planning".
Brain Storm: 15 minutes
Take two minutes tops to explain the circle. Once you've explained the rules, set a timer for 10 minutes.
Dot Voting: 5 minutes
Action Planning: 20 minutes
Unless the top vote items are really low hanging fruit (You institute a late jar for the Stand Up), the goal here is not to come up with a final plan. Instead it is to schedule the meetings and next steps for each item chosen. Final plans should be within the next week.
Total time: 45 minutes
For more retrospective resources you can also check out: