Locate the exhaust fans on your Xbox and position the nozzle of a vacuum cleaner above them. Turn the vacuum cleaner on at a low speed setting and let if run for a short while. This will remove any dirt that has accumulated on the fans, preventing air circulation and thus leading to overheating issues.
If you have set the console in an enclosed area where air cannot circulate freely, move your Xbox to a location which has better ventilation.
Make sure your Xbox is not surrounded by clutter. If that is the case, there is no way air can circulate around the console and excessive heat will build up as a result. If not attended to in time, the heat will eventually cause irreparable damage to your Xbox 360.
Check whether your Xbox has an intercooler that snaps onto the back of the console. If that is that case, immediately remove the intercooler and inspect it. The cooler might not be working properly, causing more problems than it is solving.
If you don't already have an intercooler, you might want to look into getting one. Intercoolers, if working properly, greately improve heat dissipation and prevent overheating.
Don't place your Xbox in corners or against walls, shelves or panels. It should be placed openly, with all its sides uncovered.
If you have a pedestal fan, you can aim it towards the Xbox when you are using it. Similarly, you can place the Xbox under direct air from the ceiling fan to reduce heating.
Be sure to keep the console on a surface that does not trap or absorb heat. Varnished wood or glass surfaces that are slightly raised from the ground are best for holding an Xbox. On the other hand, carpet is the worst place for the console, as it traps heat and consequently overheats the console.