I've been riding trails for about a year now and I'd like to start upgrading my bike. I have the 2011 Trek Gary Fisher Advance. I don't know where to start or what's the first thing I should look at upgrading. Or maybe it's not even worth upgrading such a low-end bike. But my question to those of you who have been riding for a while is what is one of the most common things people upgrade on their MTB's? Also, any info on type or brand of whatever it is you recommend to upgrade would by nice too. I was thinking about maybe upgrading my mechanical brakes to hydraulic? Thanks.