There are many things you can do to keep WordPress running smoothly and efficiently.
I appreciated this tip from Search Engine People in How to Keep Your WordPress Site Running Optimally:
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 would also add that fewer posts on your blog’s homepage can make it much easier for those reading on mobile (less scrolling).
How to change the number of posts on your blog
In WordPress, go to Settings –> Reading –> “Blog pages show at most ___ posts.”
Don’t forget to save your changes!