The way your post starts is important, just as the way your post ends.
SEO in a nutshell
Your blog is constantly being visited by search bots (a.k.a. spiders, crawlers, robots). Their job is to read your content and determine what you're writing about. That information is then added to the databases of search engines and pulled up in search results when relevant.
Presumably, the bots read from top to bottom. It's been said (no one knows for sure how it all works) that keywords near the top of the post are weighted more than those that come later. Therefore, ideally, you will have good, relevant keywords at the beginning of your posts.
How to start your posts
Start your posts with a strong first paragraph, or, if you use an image at the top of your posts, know that images are unreadable to the bots. Bots can only read text. For that reason, make sure you are optimizing your images:
- Rename your images before you upload them. Use keywords in your image names. Whatever you do, don't use IMG_0042 or the like.
- Be sure to use the ALT tag, again, with keywords. I typically use an ALT tag that matches the image name. (Update: Per many questions in the comments, the ALT attribute is basically a text description of your image. When you upload in WordPress, you'll see a field called "Alternate Text." Always fill this in. I usually just use the same keyword-rich name I used to title my image in the first place. See the video below for further explanation.)
- Consider using a caption and/or description too.
- Do You End Your Posts Well?
- What is Search Engine Optimization and Why Does it Matter?
- How to Use Anchor Text to Boost SEO
- Here's a video with Matt Cutts (works at Google) with a bit more description about the ALT tag (it's old, but still gives a good overview):