well, to start off, does your camera have an audio input. if it does, then you need to start using a boompole with a decent mic on it and try to always get the mic as close to the talent as possible, just outside the frame over their heads.
if money is a problem to get a real boompole. a painters pole from Home Depot with a thread adapter will do the trick. the thread adapter can be found on Ebay, look up boompole thread adapter there. i use these for antenna masts on my soundcart. you will also need to get a shock mount as well to isolate handling noise on the pole and a cable from the mic to the camera.
this is just a start, but will help