Best practice 1: Use same device
To get the best results, you want to run tests and compare result using the same device, so you remove other variables that may affect the performance results.
For example, you might want to repeat a test you did of a Login in the new version of the app and see if there are any big differences in the performance of that functionality.
Best practice 2: Similar test duration
When looking to compare two test sessions that you run manually, you should look at test with similar duration, so you can then easily compare the graphs showing CPU usage, Memory usage and FPS.
Best practice 3: Changing network conditions to uncover potential issues
When testing the performance of an app, you might want to see how it differs when you are connected to a 3G network vs a 5G network, as this might affect the experience of the end users.