Ask the person if they want someone's name in the inscription. Is it for a friend or relative, or is it a personal purchase? Always ask how the name is spelled. There are many creative spellings these days. Don't assume a spelling is Jackie, for example, because it might be Jakki or Jaqui, or any other unexpected form of the name. If you spell the name the way you think it should be spelled, and that turns out to be wrong, the person probably won't accept the book and it can't be sold to anyone else.
Signing only your name might be the best way, when reviewers say your book could become a best-seller or a classic. Unless a personal inscription is requested, some people feel anything more than the signature could decrease the value rather than increase it. Another less rigid approach is to just say something like "Enjoy reading this" and add the signature.
Adding a nice inscription often means a lot to the person buying the book if it isn't a collector's item. Short, concise phrases are preferable because long inscriptions become difficult to write in book after book. Consider something like "Hope you enjoy this book," or simply "Happy reading." Prepare a few two to four word phrases. That way you can alternate them so every person doesn't get the same one. Avoid trendy. Times change, and what is funny in one era may be terribly corny or outdated in another.
Figure out where to place the signature, depending upon the interior design of the book. Generally the title page will have appropriate space either at the top or somewhere in the middle. If using an inscription, know where and on which page you will sign so you don't run out of space. Some authors even prefer the inside cover, while others place the signature below the printed name.
Growing popularity of ebooks presents a challenge to the author relative to signed copies. A creative idea is to print just the book cover on heavy cardstock. You can sign this and either give it to the person at an organized signing or send to the buyer. If the price of the book is very low, you might want to charge for the postage.
Consider a bookplate for the signature. These decorative stickers of varying sizes are put on the inside cover of the book, but not recommended for collectors' items. They generally contain an illustration, a saying or a border and a space for inscription and/or signature. If signing an anthology of short stories that includes your story, using a bookplate you can state the title and pages of your story as well as the signature. They are also easy to mail to someone who has purchased one of your books and would like a signature.