In your HTML use CDN, which will make sure the request is not hit to your server rather a well distributed fast CDN.
Design the API to the server so that there are less number of http/https calls to a server.
Do not use loads of JS libraries. ie if you can mange with plain ES code no need to use libraries like underscore.js . Minimum number of libraries to download from the server will make the page load faster.
Try to design and implement SPA (Single Page Application), So that user need to not load content multiple times.
If you want faster partial page refreshing, use framework like ReactJS, which uses virtual DOM to make sure it updated DOM at the minimal to serve the request.
1. Use XML and Html sitemap for the listing of the different page on one place so that speed of ur website remains maintain
2. keyword and content ratio should be balanced
3. Remove unwanted unnecessary file and images