Brainstorm a list of possible topics (see 10 + 9 Ways to Find Great Post Ideas for Your Blog) and hit the keyboard. Post at least 25 entries before you begin to promote your site. Here are step by step instructions. If you're new to posting, use the visual rich editor (enabled on the Options » Writing page in the WordPress admin), which lets you add basic formatting without knowing any HTML. Note: The visual rich editor doesn't work with Safari.