Bump.

This is much trickier than one would imagine. The only way to make sure you get no quest: do not do anything.
Talking to an NPC can trigger a quest.
Being close to an NPC can trigger a quest (overhearing an NPC).
Reading a book can trigger a quest.
Looting an item can trigger a quest.
Killing an NPC can trigger a quest.
Entering a location can trigger a quest.

Things you can do without triggering a quest, to the best of my knowledge:
Picking flowers.
Killing beasts in the open world (wolves, bears, saber cats, trolls).

Things you can do to possibly bug a quest, that I know of:
Clear out a dungeon that is tied to a quest (requires waiting 30 in-game days for the dungeon to 'reset').
- Known issue with a quest to get a special helm and a Companions quest.
Clearing out Raldbthar more than 30 days before you get the quest to go to Raldbthar (the puzzle at the end resets into an unusable state).


IMO, I would just play the game and save often. If you want, you can go to www.uesp.net and look up specific quests to see if there are any known issues, and any known workarounds for the 360 (ie: not requiring the use of console commands). Just scroll to the bottom of the page to skip any possible spoilers.