First thing to do is increase C2 to 1000uF. If the power supply does not have a very low source impedance, it might help to increase C3 as well.
If there is any problem with High frequency (RF) stability, it may help to connect a small capacitor (47pF to 100pF) between the collector and base of T1.
C1 can be reduced to 1uF. That will set the low frequency rolloff to about 30Hz. If you're only interested in speech, or if you're using a small speaker with no low bass capability, then C1 could be reduced further to 100nF or 150nF.