HAVE SNACKS ON HAND
Food can be a valuable ingredient to any game, but large groups add unique food options. Tell your players to bring snacks, or award a bit of XP/gold to players who bring something to munch on. A hungry adventuring party soon becomes an unhappy one, so have options. If your group drinks, remember that beer is basically bread in terms of calories, and can hold off hunger with surprising effectiveness.
I usually suggest building a game around a meal (lunch or dinner). Everybody can chip in for takeout (send a runner and keep the game going) or order in. I generally ask my players to each bring something (drinks, chips, whatever) along with 5 dollars for pizza. After gaming for a couple hours, we order pizza delivered, and the 5 dollars generally covers about half a pizza with room for a tip.
I usually suggest building a game around a meal (lunch or dinner). Everybody can chip in for takeout (send a runner and keep the game going) or order in. I generally ask my players to each bring something (drinks, chips, whatever) along with 5 dollars for pizza. After gaming for a couple hours, we order pizza delivered, and the 5 dollars generally covers about half a pizza with room for a tip.
BE PREPARED
Regardless of how much you prepare, the party will do something that you aren't prepared for. They will kill the bartender when they get bored, ignore your quest hooks, and blindly miss the traps you thought would be unavoidable. That said, preparation makes the difference between a long and boring, frantically-researched session and a smooth session.
Before each session, I generally get a basic idea about what's going on within 1-2 miles of the party and write that down as a few bullet points. If this involves any monsters, traps, or challenges, I jot down the book/page that includes the rules I may need. If it's entirely original, I'll throw my notes (custom dragon stats, loot tables, town guard names, etc) into a folder for quick reference. I keep this list on the side since it probably won't come up, but when it inevitably comes up anyway, I have it there for reference.
POCKET SOME DIVERSIONS
When the party moves beyond where you think they were going or they move in a different direction, make sure you have a backup plan. Their guide could suffer apparent poisoning or a curse, forcing them to find the antidote to save a life. They could receive urgent word from the king/duke/count that their help is in need. It's good practice to keep a list of things you can drop on the party at a moment's notice, just in case.
Another option is to keep a list of wandering monsters handy, and throw one of them at the party to slow them down. If the party was searching for a lich-king's lair, send a few undead at them (sentries) to point them in the right direction. While I'm personally not a huge fan of random encounters, you may be able to introduce quest items to the party this way. Maybe that Troll killed a messenger and still has the note on him. Maybe a monster was carrying a weapon inscribed with the name of an NPC or family the players know. Tying the encounters to the world you have created will help create a sense of realism to the game.
INITIATIVE
Managing initiative for more than half a dozen players is just silly, and keeping everybody focused easily falls to one side. There are a couple schools of thought for this. One is to have everyone roll initiative as normal, and have the highest initiative roll go first. From there, play proceeds around the table, ignoring all other rolls in favor of simplicity. This can work pretty well, but tends to leave players feeling a bit under-powered if they end up at the "end" of the circle. They have to wait for the 10 other characters to each go as the circle creeps slowly toward them.
For some groups, this works rather well. Mine isn't one of them. Many of my players, as I mentioned earlier, are running 2-3 characters each. DCC has high character death, and by throwing more PCs at the grinder they have a better shot at surviving. To speed up initiative, I generally just have players each roll initiative with their "fastest" character. That way instead of dealing with fourteen initiative "turns" I can deal with more like seven.
In any initiative system, try to keep a running announcement of who is "on deck" to act after the current player. Anyone who isn't ready to go will have time that way to catch up with the game before the rest of the table is waiting on them.
BE HONEST, BE FAIR
Running a game with more than six players is hard. Make sure your players understand this, and they will try to make things easier for you. If you find yourself overwhelmed, it's 100% okay to say "Hold on everybody, I need to figure out what's up ahead" and take ten minutes in the middle of the session. Don't make a habit out of it, but keep in mind that it is totally an option. Your players would rather have a DM who is comfortable running the game than a DM who's scrambling to put something together on the fly.
Communicate with your players and make sure that they are ready to play when their characters need to do something. Keep a picture in your mind of what the players are each doing, relative to the world around them. Make sure that threats affect each player so that nobody feels forgotten or safe. Nothing will turn players off in a game faster than feeling like their character doesn't matter.
In any initiative system, try to keep a running announcement of who is "on deck" to act after the current player. Anyone who isn't ready to go will have time that way to catch up with the game before the rest of the table is waiting on them.
BE HONEST, BE FAIR
Running a game with more than six players is hard. Make sure your players understand this, and they will try to make things easier for you. If you find yourself overwhelmed, it's 100% okay to say "Hold on everybody, I need to figure out what's up ahead" and take ten minutes in the middle of the session. Don't make a habit out of it, but keep in mind that it is totally an option. Your players would rather have a DM who is comfortable running the game than a DM who's scrambling to put something together on the fly.
Communicate with your players and make sure that they are ready to play when their characters need to do something. Keep a picture in your mind of what the players are each doing, relative to the world around them. Make sure that threats affect each player so that nobody feels forgotten or safe. Nothing will turn players off in a game faster than feeling like their character doesn't matter.