How to add second receptacle to the same line?

I know it sounds rudimentary, but I'd like to make sure I'm doing it right.
I have two dedicated power lines with one duplex receptacle on each, that I want to add another two duplex receptacles to.
I have an idea, but not sure it's the right one. I don't really want to call an electrician for that. I installed receptacles before, so that shouldn't be a problem.
thanks in advance
In all seriousness, call the electrician. In the end it's easier than trying to explain to the insurance company how your house burned down.
One thing you could do is look at the "How To" books at your local Home Depot. Just make absolutely certain that the power is off before you do anything.