How you can improve or play around with the internal RTL SDR Dongle setting in my RTL SDR AIS Driver app or in AIS SHARE app.
Note: If you have AIS SHARE app, you do not need to change any settings in RTL SDR AIS Driver app.
Of course most important is the PPM setting.
If you have a high quality USB dongle with 0.5PPM TCXO then you do not have to mess around to find your correct PPM setting for your dongle.
More about PPM see http://www.ebctech.eu/blog/rtl-sdr-ais-receiver/
Or here: http://www.ebctech.eu/blog/find-your-ppm/
Another important thing is your antenna. The mini antenna shipped with most of the cheap dongles is good maybe for testing if you are very close to vessels. But this is definitely not the right one.
Make your own DIY Antenna or buy one
My experience showed me that you should play with DC Filter and AGC.
Note to AGC: since the dongle was orginally designed for DVB-T sticks, the build in AGC is not optimal. In urban regions this may have a negative effect.