Support what you use and enjoy. This is true in all aspects of life, including software. Especially open source software.
Here are a few simple ways to do that.
Giving a project a "star" tells the developer that you appreciate their effort. It costs you nothing, but is quite encouraging to the developer when it appears in the feed.
This encouragement is important because open source projects generally do not get any feedback when the software works well -- the developer only hears about problems and bugs.
Find the developer's email address via GitHub or their personal website, and send a quick note of thanks and appreciation. It need not be long or complex. Taking a small amount of time out of your day to do this is very meaningful and really encourages the developer.
This can be done using social media, but I encourage doing it via email because it's more personal and feels more direct. If you're big into social media, do via social media and email!
If you have the means, taking a small portion of your donation budget each year to send it to software developers who work on the software you enjoy is a great way of saying thanks. Sending a donation is easier than ever.
- If the software has an Info or About page, it might mention ways to donate there.
If none of these steps led you to a donation page, go back to option two above, and ask if they have a way to donate directly.