Improving SharePoint Site performance

If you site in SharePoint 2013 or Office 365 experiencing the performance problem,There are multiple ways to analyse and diagnostic.

Some of the important ways to improve the SharePoint site performance.

1. You can enable the developer dash board (on premise) to identify the problem.
2. Log and Event Viewer (on premise)
3. You can enable the Page Output Cache if you are working on customizations.
4. Device Channel Management.
5. Minimal Download Strategy (MDS - my personal opinion, this will works better conjunction with Page Output Cache ).
6. Running the Site Collection Health Check report is the best option to identify the bottle necks, It will reports you in problem persisted with Content type conflicting,missing parent content type,missing site template,missing galleries, unsupported MUI references (If you enable Multiple Language support feature) and issues in your custom master page and Page Layouts.

If you are running the CSOM code against your SPO site,monitor your site performance very often.

To run the Site collection health check,
Gear Menu -> Site Settings -> Site Collection health Check -> Run.