In general, to achieve the best looking video you definitely need to film in manual mode. Auto is just for convenience not for getting the best looking video. Before you go in any manual mode make sure turn on the zebra in your HV20.
Because the cinemode doesn’t appare to have as good contrast and sharpness, I would use Tv instead. But I would turn down the contrast and brightness in the custom setting in manual mode as HV20 tends to blowout highlight.
For indoor 24p at 1/24sec would be great for low light if you can accept some motion blur. I alway use the shutter priority for indoor.
For the largest aperture at certain speed say 1/24, you cover the lens with your hand for 2sec and in the mean time press exp button.
That way it locks both the shutter speed AND Largest aperture at the same time with two ND filters out of the way and the gain all the way up. Now your LCD/viewfinder will show areas of overexposure with zebras, simply drop down the exp level until all zebras are gone. The HV20 reduces the exposure by cutting back the gain and if that’s not enough by sliding in the two ND filters. You can check the shutter and aperture settings before you start taping by pressing the photo button half way down, the numbers are displayed at the lower right corner. or you can check those numbers during the playback by turning them on in display settings. To achieve a shallow DOF you need to set the largest aperture and zoom all the way in. That’s why a wide angle lens can come pretty handy, especially indoors. Talking about the indoor, another great benefit of a wide angle lens is that doubles the amount of light for the same size video frame. Because now you are standing 0.7x distance to get the same picture as it would be without it, with the inverse square law in physics the light intensity becomes 1/(0.7×0.7)=2.04. In low light this is like halfing the shutter speed!
In outdoor situations you really have many choices with HV20. If you are doing the scenery you probably want deep DOF, there is a program in HV20 just for that, or you can set a small aperture manually. If you want largest aperture you can either pick program “portrait” or set it manually. Shutter speed usually is not a problem to get adquate exposure outdoors. But if you are filming sports scenes you can pick a certain speed and then check to see the aperture is what you want. If not you can either force it open with the hand method or lower the shutter speed to close it down. Anyway in the outside without the worry of not having enough light you can play with a lot of settings to get what you want.