Sharpness actually does next to nothing on a new HDTV. It is just one of several legacy controls from the good old CRT days, that for what ever reason, we are still offered today.
You are correct though. A calibration is always necessary to have the optimal enjoyment out of viewing your TV.
Short of paying someone for doing a calibration, or if you do not have an industrial or consumer grade light meter, there are a couple of things that would at least get you on the right track.
If you have your TV in Vivid, take it off. NOW! Vivid is the absolute worst mode to have your TV on. Not only does it not output the full resolution of your TV (yes, this is indeed true) it also will usually have many "features" automatically engaged that you do not want, and can not defeat. Namely Edge Enhancement and over excessive Noise Reduction. Put your TV on Movie Mode, which is just about always the most accurate setting out of the box on every TV in terms of Gray Scale and Gamma.
Then, turn off every EE, NR, Color Corrector, Black Corrector, etc.. type feature that is currently on. Turn the Sharpness to zero. It won't make much difference, because as I said before, it is a legacy control that really has no purpose on modern sets, but since it does nothing anyway, might as well turn it to zero on the off chance that it is doing even a miniscule amount of harm.
Then set your brightness and Picture. If you don't have a test disc, you can't set it accurately, but setting it around 50 will usually be at least in the Ball Park. For the brightness, you are on your own as there is no way for me to suggest a level that will give you peak light output yet not crush your whites. This is something that you need a test disc to do. I can tell you though, that LCDs will crush whites much more quickly than a Plasma, so if you have an LCD, you might want to set it lower than what your eyes are telling you, you should to compensate.
Once you have done that, short of getting a calibration or buying equipment to do it yourself, like I have, or at least getting a test pattern disc, this is about as good as it's gonna get.
Good luck