Please do not take sandpaper or any other abrasive/cutting tool to your guitar. It's easy to take off but impossible to put back.
Adjustment of a guitar is not only personal but involves more than simply sanding nuts and saddles. If you wreck your guitar and can afford another go for it - most of us can't and appreciate that those who do know more about the interplay of different types of wood and metal and their job in the complex machine that is a stringed instrument.
KEEP PLAYING, YOU WILL GET BETTER!!!
I dont mean to the guitar it self just to the plastic inlay in the saddle. if you do mess it up my local music shop sells them for 2euro. I found this tip in a guitar magazine a few months ago helped me out a lot. when you think you have it done you just use a tuner then to tune the strings and when they are all in tune check it against the 12 fret harmonic and it should be in tune to be 100% perfect, if not perfect it will be good enough as Gibson guitars are the only guitar where this is individually done to each guitar, by hand, before it leaves the factory. Trust me you wont do any damage to your guitar because its just the white pieceof plastic you will be sanding. the guitar could be in a different room.