1. Check if the image really needs a description. Maybe it is decorative. The W3C alt decision tree(opens in a new tab) is an excellent resource to help you categorize your photos.
2. Avoid writing "Image of", "Icon of", or "Picture of". Screen readers announce the presence of an image. Adding these words inside your alt is unnecessary.
3. Keep it as short as possible. Be specific but not overly descriptive.
4. Try to put the most essential information at the beginning of your description.

“It lets me write multi-headed programs that run on 16 cores and keep them readable, maintainable, and crash-free. It also lets me write low-level algorithms requiring control over memory layout and pull in a crate that makes HTTPS requests super simple. It’s the combination of these features that makes Rust so unique.”

And the feedback from Github on the language.

A thread about Firefox that drops support for Windows 7, 8 and 8.1. It includes versions prior to 10.15 of macOS.

The author explains the reasoning and there are multiple arguments.

allyphanta11yphant teaches web accessibility, one step at a time, broken down into manageable pieces. We call these challenges. You won't need to read large amounts of text to complete those. Instead, you will learn by applying the concepts in code. Get started with your first web accessibility challenge and improve your skills.

It spots files that does not follow the XDG specifications.