Keep your case dust free, good cable management, have fans that take warm air toward a fan that expels warm air (like a fan air cycle), things such as this. There are videos/tutorials around the web.
For external cooling you'd either have to take the current cooler off to add a fan-type cooler, disassemble it to add a waterblock, or add fans to your case to create better airflow and cooler internals.
Keep your case dust free, good cable management, have fans that take warm air toward a fan that expels warm air (like a fan air cycle), things such as this. There are videos/tutorials around the web.