The render presets will give you varying levels of quality just by automatically changing the other render settings. You don't get any new variables in the presets beyond what is in the render settings window. Some of the values the presets change are the anti-aliasing values, whether GI, caustics, motion blur etc. are on or off.

One way to learn would be to change the preset and see which settings get changed. Then look up the setting (e.g. anti-aliasing) if you don't know what it is.

Or come back here to ask about a specific setting.

Edit: Also, increase the samples to reduce AO noise.