If you want to help make AdiIRC better, here is some things you can do.
Users are always looking for new cool scripts or help creating scripts.
Plugins are much more powerful than scripts and have the entire .NET framework behind it.
There is a lot of options for customizing AdiIRC, sharing a color theme/options is a great way to let other users get started.
Help translate AdiIRC into your native language, it doesn't have to be perfect, translating can be done at https://www.getlocalization.com/AdiIRC/
Creating guides to follow or documenting some specific behavior can be very helpful for other users. (Ask for wiki access if needed)
Reporting and fixing bugs is very important and helps everybody.
If you can think of a feature other clients have or something new you want to see in AdiIRC, feel free to open a issue with the suggestion.
Hang around #adiirc on chat.freenode.net or the forum to help answer questions.
If you want to donate, please donate to your favorite local charity instead, I appreciate it, thanks.