Dyson Logos is famous within the OSR RPG crowd for his blog and distinctive style of adventure maps.
Today I saw he has composed a three-part tutorial for how to copy his style.
Michael Wenman, an OSR mapper of whom I have not previously heard, decided to do the same thing.
You can even currently download Swords and Wizardry Complete for free.
UPDATE: I found a (probably illegal) web-page copy of Matthew J. Finch's free PDF A Quick Primer for
Old School Gaming, which provides a much better introduction to OSR RPGs than any Wikipedia article! Now no account registration needed to read the essay.