Well what you can do is
1. Check how many speakers you have in your car, each side should have ( 1 at your feet, 2 on the door, and 2 in the back it looks like one but if you open it theres a tweeter in it aswell..) so the same should be for the other side of the car.. = 10 speakers.
2. Find your stock AMP. should be behind the trunk lining on the left side right behind the wheel well.
3. Get a decent - good head unit, Id recommend Alpine, one of the few head units that is not over rated, the power it says it has is what it has..
4. Figure out how much bass you want, I run 2 10" JL's in a sealed box in the truck with a Power acoustics "Fire & Ice" 820 watt AMP with a capacitor (to avoid power drain)
5. find subs and have installed into a proper box or have one custom made for your trunk. (custom = costly)
6. If you do not have the ski hole behind the rear armrest of your car like I dont (didnt) and you want the base to travel in the car heres what you can do, remove your seats (they just pop out off clips) then remove the insulation, you should see a perferated line in the insulation shaped like "home plate" in baseball, also in the actual metal barrier between the car and truck you should see the same shape outlined, it is just held in place with a few spot welds and punches out with a few good smacks with a hammer, then file down the sharp edges and POOF you now have a ski hole or bass port which ever you wanna call it.. not the prettiest thing in the world but it works..
7. Drive and enjoy pissing off your neighbors with your new sound..