Disassembling the Xbox would be your best bet to be able to get every nook and cranny and really keep it clean.
Conversely, I find using a handheld vac (or a vacuum with the narrow attachment on its hose) does the trick with sucking the dust out, as opposed to simply blowing it about inside as compressed air would do. I know this matters more with say, disc drives, but to be fair, it has been one thing that's kept my old, chipped PS2 running for so damned long. At least with a vacuum to do it, you're removing the dust from inside much more actively.