i would absolutely break it open and blast it out with some compressed air, from a can, not an air compressor (they have a small amount of moisture that comes out with the air), because all that dust is a heat insulator. it can contribute to overheating. i'd do the same blasting to any orifice i could see/find and would even do the same to the disc drive with the door open. however, right after that i would use a laser lens cleaning disc to get the dust off the laser lens reader.
everything destro suggested is very good as well, though i do think that the vertical position allows for much more airflow and contributes to a cooler running 360, in my tv stand/setup, it's not possible to run vertical.
whatever you do, don't get one of those nyko intercoolers as most of them don't have their own power source. they draw power from the 360, which causes more heat, and some have been known to actually melt to the power input at the rear of the system box.
also, any game you're planning on playing, INSTALL TO THE HARD DRIVE! (not all games can be installed, FIFA 13 for sure and others)! it prevents the disc from spinning up during play, it might still on startup, and no spinning discs means it runs quieter and cooler. both good things.
good luck with the long life on that bad boy