The description on your homepage should tell your readers why you are writing your diary online and what they should expect to find on your site. This should not be about you because you should have a separate biography page for that. This should just be a brief welcome message.
Keep in mind that this is one of those things that will either make them stay, click through to your entries and start becoming a fan of your site, or make them click their back button. You need to say something enticing that will make them want to click through to another of your pages. If all you say is "Welcome to my site" then they will have no reason to go any further.
Try to find something about you, your life or your beliefs that you have written about in your entries and mention that. Don't tell the whole story here, only tell just enough to get them hooked.
If you have a hobby that is unusual or something that is popular you can use that. If you like dogs, and intend to talk about your dog a lot, then write a part of this to dog lovers. If you like deep sea diving and intend to talk about your adventures under the sea, use that. If you are willing to help people with their problems about a specific thing then mention that.
Tell your readers how often you intend to update your site. Let them know when and where they can find new and old entries. If you have a forum (bulletin board) or chat room tell them where it is and let them know that they are welcome to use it.
If you have a Webcam make sure to post a link to it here as well, they are very popular. Pictures are also very popular so if you have any of you, your family and friends or your adventures in life then also make sure you tell them where to find them.
Remember to keep it brief, not longer then one screen size. Break it up into small paragraphs too. This will make it easier to read and will keep the reader's attention longer. That's important if you don't want them clicking on their back button and leaving your site forever.
