Sometimes your ambient noise (where there isn't talking) is a bit noisy
Select a section of background noise and go to "Effect > Noise Reduction". Click "Get Noise Profile"
Now select your area you'd like to reduce noise from, and go into "Noise Reduction" again
Now adjust your numbers until you get them how you like them and hit ok
This will try to remove the pattern of your ambient noise profile from the track. A side effect is that it can make the audio lower. To compensate, you can select the dialog you want, and go to Effect > Amplify
The default value will be the most it can be magnified, so I usually put it a little under default, and then say OK
I would then select the tail end of the clip and go to "Effect > Fade Out", and do the same for the beginning with "Fade In"
you can select any ambient noise around and lower the volume to nothing with "Effect > Amplify", and then just give it a negative number.
When you're done, select the clip in particular you want, and select "File > Export Selected Audio"