The first step is to determine the root cause.
Cache and CDN
Using a caching plugin is one way to optimize site performance: WP Super Cache
With a caching plugin, you can also use a Content Delivery Network (CDN) and/or Cloudflare, Jetpack Photon, to further speed up your site.
Be careful though. Caching plugins also have the potential to cause your site to load incorrectly or not at all, if configured in an incompatible or faulty manner. Confirm settings after implementation.
Contact your hosting provider and discuss the impact your hosting plan has on site performance. Quality dedicated hosting is preferred over cheap hosting on shared servers. Our recommendations at: WordPress Hosting Solutions.
A front-end cause of slow site performance is image size. The file size of your product/blog images directly impact the speed at which your site loads. A tool like WP Smushit can help optimize images within WordPress.
Also refer to this WC Image Guide.
It might be necessary for you to increase the memory limit as explained at Increasing the WordPress Memory Limit.
A site’s sluggishness could be related to plugin load.
To test, deactivate all plugins and reactivate each one by one until you find a potential cause. You could also use the Plugin Organizer to control the order of activation and toggle plugins on/off on a per page/post basis and by mobile.
To test your theme, temporarily switch to the default WordPress theme and navigate through the site. If there is an improvement in performance, the problem is likely related to your theme.
Additional Tools and Tips
- Offload all unnecessary functions from your web server to another server or third party service, such as email being sent through a dedicated SMTP provider.
- Web Performance Optimization Tips