Ok, so here's my ghetto real quick writeup for an amp install in a non-BMW or BMW with the batt up front.
The first step is to decide where the amp is going. In everything I build, the amp is usually integrated into the design. Amp location is important, as you need to be able to ground the amp securely as well as attach the amp securely.
Once you know where it's going, you need to run the power wire from the battery to the amp. If you cannot find a hole to poke the wire through, you need to drill one.
You should also use a grommet or some for of sealant around the wire to keep it from chaffing.
For methods of routing cables, refer to my other audio DIY. Most cars are the same, and you will either need to pull up or unscrew the trim, then slip the wire underneath. In the case, the glovebox was removed to drill the hole, and the kickpanel as also removed for better access. The door sill trim wasn't removed but rather unscrewed and pulled up to route the cable.
Once the wire is run, connect it to the amp. When using a thick wire, you can flatten it with a hammer to make the amp accept it easier.
Now your positive wire is hooked up. To connect the ground, find a nearby bolt or screw connected directly to the body, and use a ring connector to attach it. Use the same method for the battery. (If you cannot find a bolt to use, then you need to drill a hole and connect it with a screw. Make sure to scrape away any paint to ensure a solid connection.)
Here is a shot of the battery hooked up. Note the ring connector. You will also need to install a fuse holder. You should do this before connecting the wire to the battery.
Now you need to run your RCA/Remote turn-on lead. You can run both down the same side, but it needs to be the opposite side of the car as the battery wire. As a precaution, you can run the turn-on lead on the same side as the battery line, but it rarely causes interferance to run it with the RCAs. Connect these up to the HU (conect the turn-on to the blue/white wire) and connect to the amp. The amp should now turn on when the HU is on.