First, there is lots of good information out there, and I am not an expert; but I'd like to share what works for me in case others find it useful.
Here are two good examples:
I'll talk about two approaches, and then discuss some background and math (just skip the math if you're not interested).
We want to do this because:
We've got two goals: a 1L starter and 0.5L of overbuild for next time
Same goals as above, except that we opt for quick and “dirty”.
Have followed one of the procedures above you're now ready to either swirl the flask/mason-jar every once in a while (whenever you think of it) or use a stir-plate
Now you've got 1.5L of starter.