I regularly run into the same scenario when training users on AT, which prompted me to do make a little note of it here. For some reason too many trainers forget to go through the very basic issues of the operating system their working with, before they start explaining the hotkeys of the AT. This results in the user not realising how to effectively navigate and control his system.
A typical issue in Windows is that the user doesn´t know about the alt-tab hotkey. A very simple thing in itself, but if you don´t realise that almost every program is run in a separate window and that you can switch between windows using the alt-tab hotkey, you are creating more work for yourself than is necessary.
Again in Windows, another example is failing to explain how the desktop is structured. Yes, there is a desktop and yes there is a Start menu. But, if you don´t mention the system tray and explain why it´s there and how to navigate to it, windows-b, you really haven´t explained everything, have you? I´ve worked with users who have had a screen reader for, in some cases, years and didn´t realise that they didn´t have to navigate to the control panel and all the sub-categories there to find their wifi connection.
Always discuss with your user first what it is that you will be concentrating on in the training session. Make sure you are both on the same page, and in the same book in that regard, and last but not least: Do not forget the practical issues.