Best way to install amp and subwoofer in car?

I just got a amp and a single MTX 12" package and I got the amp kit for it. Im just wondering what the best way to hook it up, i guess to the car speakers. I was thinking of connecting the speaker wire by tapping the rear speakers through that plastic column thing thats comes off in between the front and rear doors. I got a chevy trailblazer 06. I heard you might get more power with the front speakers..? Is it better to take out the radio, cuz i would rather run the wire from the back, or how do you run them from the radio? i have basic instructions and youtube videos but other than that i have no idea what im doing, so any info will be of great help. thanks.