Jeffe & James talked about logistics and preparation. I'll take on the actual "ink on paper" suggestions. Here are my Top 5 Tips for Signing Books:
1. Archival Ink Pens: Sure that roller-ball gel-pen is comfy to hold, but it smears. By the time you're done signing, your hand looks like a Pollock painting. Archival Ink Pens shouldn't smear, bleed-through, or run when encountering wet. Bring 4, one for your backup, one to share with the frazzled author signing next to you. Oh, and go for dark but bold color--as in other than black. Get a pack at a craft store -- Michaels sell a 4-pack for under $5.
2. Personalization: Ask To Whom You Are Signing the Book & How to Spell the Recipient's Name: It's not uncommon for folks to ask for a signature on a gift. Always. Always. Always ask how to spell the name. I don't care if they say, "Tom" or "Sarah" or "Bob" never assume you know how to spell it. Even if it makes you feel like a feeb, ask. Don't crush a fan's enthusiasm just because you assumed you know.
Note: A variation on this is to bring a pad of post-its and have the reader write down the name. This is particularly helpful if you're signing in a crowded place where hearing the person 10-inches away from you is challenging.
3. Have 3-5 Short Go-To Messages & Rotate through Them: If you're lucky, you're going to be chatting while writing. If you're smart, you've practiced writing these signature messages over and over and over so they happen with muscle memory more than conscious effort. Most importantly, you don't trip up yourself with misspellings.
4. Personalization: Book-Themed Greeting or Closings: Level-up your personalization by incorporating the theme of your book/series into your message. Writing about Spies? Give them a Special Spy Code Name. Writing about Clans, Tribes, or Houses? Assign the reader to one from your book or make up a new House Name just for them. For example: YA Author Jenn McGowan wrote a YA Historical Series MAIDS OF HONOR. Each book's title follows the pattern of "Maid of [Description]." When she signs the book, she asks the reader what their passion is, then combines the title pattern with the reader's passion. I've a thing for shoes & sharp knives, so my personalized greeting became "Maid of Stilettos."
5. Personalization: The Reader-Requested Message: A Caution: When a reader requests a specific message, be aware of atypical humor, the double-entendre, and content that clashes with your professional persona. What might be funny to a reader could be offensive to you. What is an inside joke between friends, may be too easily misconstrued. You do have the right to "edit and revise" -- or patently refuse-- to write what they've requested. 98% of readers are awesome and will never put you in this potentially awkward situation. Your name. Your signature. Your right to say no.
There you have it, 5 Tips for Signing Books.
READERS: If you are the reader getting your book signed, be a fabulous fan and have your name and any special message legibly written on a scrap that is at least as wide as your palm. Assume all authors have wretched eyesight. We'll thank you for it.