Here are some things you can do to fix your problem.
1. Only use a Hardwire connection for XBL (Ethernet Cable)
(As Ourenge said but it. It's like $3-$10 depending on length and if you bought your X-Box new, it came with a free 8' one.)
2. Don't play X-Box with shitty internet to begin with. Sooo.. I guess make sure you have decent internet to being with.
3. While playing XBL, don't be downloading videos/pictuers of naked underage boys (PRRROOONN) (Fucks up your connection horribly)
4. Make sure no one ELSE is downloading anything, the more people on your internet the worse off for you. Especially when you're on wireless.
Now if these are all as I have said, then reset your Modem and Router.
Turn em both off at the same time and then restart your Modem. When that's done then restart your Router.
Iso Don8tion for helpz.