Website performance
Website performance is critical to engaging your audience. Nobody likes to wait more than a few seconds (or maybe milliseconds!) for your website to show them the content. Today, there is a diverse collection of technologies, tools, platforms and content providers that make up a given website. To improve the results for your website, you first need a baseline report on exactly what's happening "today". Go over to https://www.webpagetest.org and get a test result. Then you'll have a good idea of what needs to be addressed and you'll be able to put together a strategy to improve your website. Your audience, and your site funders will both appreciate it.
Caching
Caching can have a great effect on performance. There is server-side caching with caching servers like Memcached, Application caches like APC, Database server caching, and also client-side caching when you configure the web server to set 'expiry' headers on static content so that the browser uses it's local cache instead of requesting (old) elements from the server on each request.
CDN
Content Distribution Networks (CDNs) are a technique to employ if you've got a geographically dispersed audience.
Compression
The web server can be configured to compress a response when the client browser is able to decompress.
Optimization
The optimization of web images used to be one of the chief aspects of web performance. It is still important. Do not serve a desktop wallpaper as a background image without at least optimizing the image.