The main and most important part of teaching computer use to absolute beginners is to ensure that they are not made to feel any apprehension. Also, from personal experience, I know that a down-to-earth attitude from the part of the trainer/teacher is paramount.
If at all possible, allow some time for the trainees/students to have some refreshments and mingle with them to break the ice. Make them feel at ease. Be polite, cheerful and friendly, get to know a little bit about them first, make a short conversation with them that does not initially revolve around computers, crack a joke, say how you also were once a beginner. Offer words of encouragement and support.
For one-on-one training, again, be cheerful, offer them something to drink, converse, tell them that you are ready when they are ready to start. Sit next to them (do not stand behind them or over their shoulder).
Ask if they are comfortable and if they have any concerns or questions before you start. Always be encouraging and supportive. Tell them that they should not worry if they do not get it from the word go, that this is normal. It will get easier as they continue to use it and become more familiar with the system, and in any event they can always ask you if they needed any help and support. Explain its general use and benefits.
Provide them with your pre-prepared manual, a step-by-step guide that will cover all aspects of using the computer, from switching it on to using the software to switching it off when they have finished. Your guide should be simple with diagrams and clear numbered instructions.
All along, try and compare the computer and its components to something they are bound to be more familiar with. For example, pretend as though it were a television, and show them how to switch the computer on from a button just like the television, and how a picture appears once it is switched on. Compare folders as being filing cabinets and computer files as the real paper files inside the cabinets. Explain how files are named just as paper files are labeled, etc. This will also help them learn and remember the terms used in IT.
Go slowly, show them how it works, repeat the steps if necessary, let them have a go, ask if they are having any problems and repeat the process again if necessary until they can do it themselves. Try different ways and explain further if need be.
Summarize the process in simple bullet points. Make sure you very clearly explain the don’ts (the fatal errors) that should be avoided. Ask them for their views in general and whether they have any questions before you conclude. Remind them to use your easy, step-by-step user guide and refer to it as and when necessary. Reassure them that it will get easier day by day and that they should not be scared to search, find out and try certain system tools themselves.
Finally, praise them for their hard work with a big smile!