There are many things you can do to keep WordPress running smoothly and efficiently. I cover some of those things here.
A post from Search Engine People called How to Keep Your WordPress Site Running Optimally showed up in my reader recently and I appreciated this tip:
4. Avoid Over-stacking
While it may be tempting to call up a lot of blog posts and stack them on your homepage for all new visitors to see, a large quantity of posts will result in a page that takes a long time to load. This is further exacerbated by posts which have a lot of multimedia content, such as high-resolution pictures, mp3 files and videos.
I just reduced my homepage excerpts from the default 10 to 6. I'm not sure it makes a huge difference in loading time, but I like the less cluttered look anyway.
How to change the number of posts on your homepage
If you're using WordPress, go to Settings –> Reading –> Blog pages show at most ___ posts.
In Blogger, go to Settings –> Show at most ___ posts on the main page.