what are best practices for showing help information

I would like to put fairly extensive help information within my app - both "how to use" and explanation of what one is seeing.

The app (map oriented) has a row of buttons at the bottom, and I was considering adding a help button.

Context sensitive help is mostly not appropriate, btw.

What are common and best practices for this?

Thanks

I wouldn't suggest using a help button, once the user knows how to use your app it will be useless, and will only takes some space.

What I do (but it's maybe not the best practice) is to show a popup on the first use. Within the popup I put some basic help and a link to my website which fully explains how my app works (with some screenshots to make it user-friendly). I also put a "Help" button in the activity menu which redirects to my website again.

What I can suggest is to explore by yourself how other android apps shows the help information, and reuse or adapt the one you prefer (this is what I've done).

I have put help into a menu item as I expect new users to click the menu button anyway (my app, Zwitscher also has a button bar at the bottom).

Clicking the menu item then starts an Activity that simply shows a table view that explains the various buttons in the system and contains a link to more information online. See https://github.com/pilhuhn/ZwitscherA/blob/master/src/de/bsd/zwitscher/HelpActivity.java and https://github.com/pilhuhn/ZwitscherA/blob/master/res/layout/help.xml

Another option I've seen sometimes is including a help option in the preferences/configuration screen.

Usually it starts a new activity with a sequence of steps to make the user understand everything.