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 customising AdiIRC, sharing a color theme is a great way to let other users get started.
You could 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 behaviour can be very helpful for other users.
Reporting and fixing bugs is very important and helps everybody.
If you can think of a feature other clients have and AdiIRC is missing, feel free to suggest it.
Hang around #adiirc on chat.freenode.net or the forum to help answer questions.