Check your server is well located and run GT Metrix reports from multiple locations
If latency is an issue implement Cloud Flare
Check if the server is HTTP 1 or HTTP 2
Check All images on each page using GTMetrix and replace an bad sized images
Check the performance of HTML and other server settings
If we have HTTP/1 we need to use WP Rocket to combine all files and get a better page speed score
Audit your WP Website and remove any unused plugins
Some further optimisations for WordPress can be done to get faster page loads.
Basic page speed is complete.
Setup an Alert for GTMetrix.
Whatever time you have got as you average over 10 hits set an alert of maybe 0.5 seconds but no more than 1.0 second from your best time in GTMetrix.
Create an alert.