[Powerlord]

That depends. If it's a public plugin, the first thing I do is start a new GitHub repository for it.

Then I copy the plugin_template.sp from my sourcemod-snippets repository and start working on the new plugin in NotePad++.

I do testing primarily on my test server (mentioned in my signature) especially for game modes that are arena-based... said test server currently costs me around $10/month.