"What happens to my mid-tones? I set exposure using exposure meter; open the shot in Adobe Lr (or Adobe Camera Raw, or some other converter) - the shot looks overexposed and everything starting from mid-tone and up looks very flat. If I shoot RAW+JPEG, JPEG looks OK, while RAW is not. Should I expose lower?"
Please don't lower the exposure, you will be underexposing by more than 1 stop additionally to the underexposure due to camera meter calibration. Not a great idea, especially if the light is low and you are already above ISO 400.
Instead, change the default settings in your raw converter (read on for a suggestion) or adjust on a per image basis. Having customized defaults, however, will save you a lot of time down the road.