1. Form Design

• Keep to less Fields on the form.
• Keep to 5 Tabs or Less in the form.
• Place the most important attributes in the first tab on the form, and collapse tabs where possible
• Collapse all Tabs on form load except the main first Tab.
• Use Quick view forms to show related entity data instead of creating new fields and mapping same data for viewing purpose.
• Forms can have Web Resources embedded into them which can be used to display custom content (i.e. images, html pages etc.). These also increase Page Load times – consider putting these into collapsed tabs also and whether they should be rendered on a mobile client or not.
• Create Organization type of entity instead of User/Team owned entity when you don’t need any owner of the record.

2. Sub Grid

• The number of columns should be kept to a maximum of 5/6.
• Sub grids should be (recommended) placed in a Collapsed Tab.
• Make sure you are setting minimum record per page.

3. Plugins

• Identify the synchronous plugins and make them asynchronous as much as possible.
• Check all plugin code having context depth check if you are doing similar operations.
• Ensure you disabled plugin trace log configuration by navigating Settings -> Administrator -> System Settings-> Under customization select Off or Exception. Enable this setting when you want to debug/fix any issue as per your needs. 

4. Workflow

• Identify the real time workflow, convert them to background workflow if possible.
• Make sure all the workflow having Checked “Automatically delete complete workflow jobs”.

5. Data Query Optimization

Identify the query in your JS/HTML/C# code where no column defined in the select operation. Make sure you defined fields which needed in each select operation instead of having all columns–

• FetchXML
• Web API
• Query Expression
• OData with Organization Service call
• REST
• XRMServiceToolKit

6. Minimize Field Level Security

Identify what are the fields level security applied in the forms fields, if there is any unnecessary field apply for the entity which you don’t need to remove the field level security from the fields. Using FLS provides several benefits in terms of providing more precise control over the data that specific users can access and view. However, there is a performance impact associated with using FLS, and the more extensively the feature is used in an implementation, the greater the impact on performance.

7. Unnecessary Audit Logs

Disable entity level Auditing –

We should enable auditing on those entities which we need. To find the entities which are enabled for auditing, navigate to Settings -> Customization  -> Customize the System -> Select Entities, In the list sort by Audit Status. Disable the entity auditing which you don’t need.

Disable field level Auditing –

Navigate to Settings-> Customization – >Customize the System -> Select Entities which are enabled auditing -> Navigate to fields form left panel. To disable the field auditing, double click on the fields and it will navigate to fields properties where you disabled auditing by selected disable options.

8. Record per page.

Under user’s settings called ‘Record per page’ which we can modify on a per user basis. Make sure the default defines 25 or maximum 50 records in Dynamics 365 grid. Navigate to corner gear icon and then options –> Under General tab you will see the records per page.

9. Increase Browser Disk Space

Make sure that Internet files for Microsoft Dynamics 365 are not being deleted, increase the disk space for temporary Internet files.

• Open Internet Explorer, and on the Tools menu, click or tap Internet Options.
• On the General tab, in the Browsing history section, click or tap Settings.
• Set the Disk space to use field to 350. The default value is 50.
• Click or tap OK, and then click or tap OK again. 

10. Retain Browser History

1. Open Internet Explorer, and on the Tools menu, click or tap Internet Options.
2. Click or tap the General tab, and in the Browsing history section, make sure that the Delete browsing history on exit check box is cleared.

Hope this helps :).