One of the most effective ways to reduce hiss and background noise during silent sections (between words and sentences) is to use a Gate Plugin, in Audacity this is called the Noise Gate. The idea, if you use it, is to adjust the level reduction to a low, but not silent level. Try different settings, see what works for you.
Sound on Sound magazine has a good writeup on ReaGate, the Gate plugin that ships with Reaper, my preferred DAW.
It is ALWAYS best is to get your mic as far away from any source of noise, as they are extremely sensitive. A big culprit for noise is your fan on your computer. Make sure your computer runs as quietly as possible, or move it away from your microphone.
You can get super long USB extension cables
