This is a very simple tutorial that could help you with the performance of your custom modules. I will show you how to use Cache API in Drupal 8 and Drupal 7.

You don't have to perform heavy caluclations every time you need to pull data either from third-party API or from database. Instead run it once and cache it. I personally use caching when I need to run complex SQL queries and third-party integrations (Example: get a list of available forms from Hubspot, or available campaign lists from Mailchimp etc).

In Drupal 8 use the following code structure: