There are various things you can do to improve performance and take additional burden off of your machine or device. See the suggestions below.
KEEP IN MIND: If the device or machine you're using is low on available memory, these can sets help, but like any other app, Sketchbook will be hampered by low device memory and may have problems. We recommend you free up memory by backing up your content to the cloud or another external source.
Improving performance on Sketchbook Pro for desktop
Your preferences are where you can benefit the most. The first thing we always recommend is to turn off Enable Rotate Canvas. When working with an extremely large canvas, you can experience slower performance when enabled. Turn this option off can make a huge difference. See Preferences for instructions on how to do this.
Another preference to turn off to improve performance is Display brush stamp. This displays the stamp of your brush while drawing. You can also experience a lag in performance when using large brushes. Therefore, if you are using large brush, we recommend you disable this option. See Preferences for instructions on how to do this.
Two last things you could do would be to reduce the default canvas size and reduce the maximum number of undos.
If you are experiencing issues with Sketchbook Pro freezing or crashing on a secondary monitor, please read this article.
Improving performance on Sketchbook for mobile devices
Your preferences are where you can benefit the most. The first thing we always recommend is to look at your canvas size and layer usage. If you don't need to be working with an extremely large canvas with a lot of layers, select a smaller canvas size. Since a larger canvas and layers can take its toll on your device's memory reserves, this can greatly improve performance. If you really need to be working on a large canvas, try restarting your device to free up RAM that was in use in the background, to make more available to working with this file.
The other thing you can do is turn off Rotate Canvas. When working with an extremely large canvas, you can experience slower performance when this is enabled. Turn this option off can make a difference. See Preferences for instructions on how to do this.