Disconnect issues are tough because there are so many possibilities. you really need to do some testing to narrow down the problem.
1. If you use wireless, try connecting on a wired basis temporarily, just for testing purposes. See if you still experience the problem. If it goes away, you know your wireless connection is the issue
2. If you use a router, try a direct wired connection to your modem. If the problem dissappears you know you need to look at your router.
3. If you experience the problem, even direct connected to the modem, and you have DSL, make sure you do not have a "filter" on the modem line.
4. If you have cable, make sure your data line does not go through to many "splitters". Each splitter weakens your signal and to many can cause issues.
5.If there is no filter or you have cable, then you need to talk with your ISP. Have them come out and check your installation and possibly give you a new modem.
6. Some people have reported that doing the harddrive maintenance on their xbox has solved some disconnect issues. Can't explain why this would help unless some kind of corruption in the profile causes some timeouts. But some people claim this has fixed
their particular problem.
But there are so many possible issues,without doing some testing , you can't really know what steps to take.
Try the "connection Troubleshooter" at support.xbox.com/.../NetworkHelp.aspx