What types of stuff is he lying about? not that it makes much of a difference cause a lie is a lie but if it's mostly small things to get attention then you MIGHT have to pull back on some of the attention as he might be 'relishing in the moment' so to speak
punishment ... of course this depends on the types of lies, the extent to which he is lying and how often ... ground him, pull back some of his privileges, take away certain items he may treasure (computer games, camera, etc ... don't know really what he has so just making suggestions here)
but ..... again it depends on what he's lying about ... if its about everything from small to big stuff then organise to get him some help ... get someone who can speak to him to find out if something is bothering him and he is just acting out of frustration because he can't tell you the truth
Just woke up and typed this at the top of my head so if it seems jumbled please forgive me
lol
xxx Lisa xxx