Here's some general things that I have found useful to do to prepare for RTEE (currently on its 16th session!) in no particular order
1. For the first session, prepare a map of Hommlet. Not the crappy one that comes with the module, or the larger but still crappy one from Dragon. You don't have to be a genius mapmaker, but make it look slightly interesting and have names of stores instead of numbers. With a map on the table, players will be much more likely to explore the town.
2. On your first read through, keep an eye out for the following (they can be elusive): important pieces of information that the party needs to find out, ways in which the party can get from one section of the adventure to the next, things that will happen in one place based on player actions in another place.
Tag those pages (or make a list) because the module does not have an index and they can be a pain to locate mid-game.
3. On your second read through, make a rough timeline of events that would normally take place without player intervention. Modify this timeline as you play, according to what the players do. Also, make a rough "heirarchy" of the bad guys. Who makes the decisions, and who follows orders. Put a star next to any "free agents" or bad guys who have their own agenda.
4. Make sure that your players know that this is, for the most part, a highly lethal dungeon crawl before they make up their characters. Having mounted combat is not going to be too useful here. Having someone who can find traps is

Set up rules for what happens when someone's character dies, because it will happen.
5. Take extra care in breathing life into NPCs! The endless run of combat can be a bit wearing, even on hardened hack-n-slashers. Use the opportunities for roleplaying to their fullest and encourage players to make well-developed characters by offering subplots that are fun and useful. Watch out for signs that the party is falling into a rut so far as strategy goes. It usually either means that you aren't making the battles tough enough (or interesting enough), or that the players are about to all die in the next tough fight.
6. Leadership is a fun feat, and there are a bunch of NPCs designed to be potential followers. Think in advance about what good combinations might be and have NPCs be willing to follow the PCs on their quest. It will add to the party's survival chances, as well as adding more opportunities to roleplay.
Hope this helps
Balsamic Dragon