Audacity - Improve your voice in audacity

1 Effects > Noise Reduction
2  #step1) select only a part of the background noise to get noise profile:
3   select some noise and press "Get Noise Profile"
4  #step2) select all track then filter the audio:
5   Noise Reduction(dB) : 12
6   Sensitivity : 9
7   Frequency smoothing : 3
8  #step3) if background noise still hear:
9   do step1) and step2) again

1Effects > Truncate Silence
2  #adjust settings
3    #defaultDuration: 0.5S

1 Effects > Bass and Treble

1 #step1) reduce the loud parts using limiter:
2   Effects > PlugIn 1 to 15 > Limiter
3   #use one of these 2ways that suits the most: (change the "LimitTo" values according the you sound track)
4    #way1)type=Soft Limit, LimitTo=-9.00 (I mostly use this way) 
5    #way2)type=Hard Limit, LimitTo=-10.00 (This way is the best for balancing loud and quieter parts, and for reduct loudness in normal sound tracks)
6 #step2) then reduce or increase the track loudness
7   Effects > Amplify > Amplification (-1.3) #toDecrease
8 #step3) you can also increase the base of an high pich track
9   using Method3

1 #step1) make loud parts quieter using Method2 > way2
2 #step2) increase the Bass and decrease the Output Sound
3  Effects > Bass And Treble
4   #Adjust Bass(10db), make treble at 0, make Volume lower,
5   #then test Bass using "Start Playback", look at the monitoring bar, if output rate in yellow or red then decrease the "Output Volume" and test again 
6 #Other persets to try:
7  #preset0) #Bass (dB): 0,Treble (dB): -12
8  #preset1) #Bass (dB): -15,Treble (dB): 10,Volume: 4
9  #preset2) #Bass (dB): -15,Treble (dB): 0,Volume: 4

1Effects > Compressor
2(you can adjust these values to improve sound quality):
3e.g: 
4 Threshold: -30dB
5 Noise Floor: -50dB
6 Ratio: 5:1
7 Attack Time: 0.20
8 Release Time: 1.0