How do you boost up my V6 Ford Mustang?

If by "boost up" your V6 Mustang you mean increase horsepower, you're in luck. While there is not as much aftermarket support for the V6's as there is for the V8's it is still out there and available.

For your first mods I would recommend a cold-air intake, exhaust system and tuner. A K&N intake like this one would be great for a 99-04 Mustang:

http://www.americanmuscle.com/kn-cai-9904-v6.html

However for an 05-09 'Stang I would recommend an intake/tuner combo kit. A tuner reprograms your car's computer, working with your modifications, to produce the most horsepower (or mpg's, depending on the tune). If you're unsure or are unfamiliar with tuners these articles should help:

http:/www.americanmuscle.com/simple-guide-chips-tuners.html

As for an exhaust, you should look for a true dual exhaust setup. This replaces the restrictive factory Y-pipe with a freer flowing "X" or "H" pipe. There are mid-pipes available that allow you to use a GT catback which would give you a lot more options and would be my personal recommendation.