old school for me was very free form, or dungeon crawls, though those were rare for me (my dongeons tend to have a reason to exist, such as locking away a crature or magic item).
When I started, I created maps that covered a large area, placed terreign and city states and kingdoms and mountain ranges, rivers, lakes, wildlands, etc. Notes on locations were sparse: Cassidine, a Kingdom ruled by the warrior Iconoclast, yet lacking much formal law. Highly values freedom, tends heavily towards worship of benevalent gods...Arcus, a kingdom ruled by the mostly kind but egotistical Don parnell, dominated by the castle Arcanum, all law flows from the archmage, which tends to end with a Hellbomb Burst cast at level 99...
My players freely wandered as they wished. I rarely had an intial adventure planned. I let thier decisions and random encounters develop the story and create a story arch, operating under the idea everyone and everything has a reason behind it. Quite often, the players handed me the plot and I simply shaped it on the fly. As the GM, I focused on vocabulary, places, names, histories, magic items, creatures, and wove them into an adventure/story. My worlds were fairly cruel, violent and dangerous. Death of PC's was not uncommon.
My first MERP module was Rangers of the North, then Court of Ardor. They were perfect for my style. So much good detail, names, languages and backdrop. Also lethl. RM became my game and I left RQ for it.
Truth be told, I remain always the GM, and my free time aint what it use to be, so I find myself regressing to those early days of freeform. SW is my prefered setting, but I ran a middle earth based game just a few months ago. I have highly developed worlds with lots of good lingo and places that can draw the players in, which has always been my goal number one; entertain the players. Thats about as old school rule as there is I guess.