Well it's different depending on what style it's in. If it's classical, then try to nail something like The Chaconne by Bach (good luck, it's 20 mins long [except segovia's edition] and would need to be memorized, and is rated a 10/10 on difficulty). If it's Jazz, there are alot of standards that you can make great, like Autumn Leaves, for example.

But if it's rock, I couldn't tell you. I've never really liked rock music that much, other than the jam-bands (phish, grateful dead, etc). I don't even listen to those guys anymore, so I'm not sure what to tell you. But if it's called Guitarmageddon, then probably whip out some tapping or something lame like that *Attention All Tappers, don't start bitching*.

~Incidents