Since the 2009 editions, Norton users have been able to set their their idle time so that Norton will not run background tasks until a set amount of idle time has passed. Setting it to about 20 minutes is a good way to ensure it will not start to run background tasks while you are browsing or using other programs. Also, turning off compressed file scanning will reduce load time a little bit. Another trick is to turn off the early-load feature in your auto-protect options. I do not recommend doing this unless Norton is using more than 50% of your resources, as it can reduce your system's level of protection.
Norton has also provided a tool called Norton Insight to check what is dragging down system performance, and gives users the option to reduce the number of files that Norton will constantly scan for viruses. Without any change in settings, Norton will automatically assume that all your files are a risk. Using this tool will allow you to tell Norton which of your files are low-risk, reducing the program's workload and freeing up system resources, so you can get back running to your first-person-shooter or MMORGG in full HD graphics settings.
In order to get the most out of Norton Insight, you will have to instruct it to disregard all but the most critical files during a quick scan. This can vary per user, but I would recommend keeping core system files, any folders where you share files, your download folder, and your browser registries. A corruption of your system registry could lead to catastrophic system failure, and those other folders are where viruses and spyware most often infiltrate through.