You should start by changing out your factory speakers. Look for some that have a high sensitivity rating, such as Infinity. Your factory speakers won't handle a big amount of power, so I wouldn't amplify them. You will get better sound with aftermarket speakers, and if you want, you can add an amp to those later for even better sound.
2002 Ford Focus Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs
Magna:I have a 2005 Accord EX coupe and was reading online that many come with a 180 watt amp (which is weak) but I was wondering if its easier for me to use the existing wires for a new powerful amp. I dont feel like I can wire the whole car myself properly.
Depends how the 180W breaks down. If that is 45Wx4 Peak, then you might have better luck, an easier install, and more features just replacing the HU.
If you just want to upgrade the amp, you can probably get away with using the existing input wires (to a LOC if your amp doesn't have speaker level inputs) and existing speaker wires, but you might need to run a new remote turn-on from the fuse box, and I definitely would recommend running new power and ground wiring.
Hope This Helps!!!