I actually use a $24 dollar headset and the quality is quite alright, but if you wanted to get more serious I'd reccommend getting a Blue SnowBall Mic, it doesn't cost too bad and it sounds great.
As for actual acting, try to first master your natural voice then eventually try out for roles out of your range instead of the same type character over and over again. Also, try renacting scenes from movies or whatever by yourself trying to sound like those character and deliver the same emotions. I may sound crazy to my family talking to myself, but atleast I'm improving my acting. Also, drink room temperature water and plenty of it.