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.
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I'm sure you've figured it out by now, but it's very simple to add another receptacle to each line. Figure out where you want the other receptacle, shut off the power to each line, and run new wires from the old to the new receptacle. Match wire size, and go from the "hot" side on one to the same location on the other one, neutral to neutral, and ground to ground. Since you've done it before, should be no problem, and you won't have burned the house down.
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Mental? ok, but you make sense. (sometimes sadly lacking in these forums (fora?)
Maybe in a strict technical terms it's not dedicated, but it is dedicated as far, as nothing else is on the same line