How many pillows you sleep with is entirely up to you. It's more a matter of comfort than style. However, when making your bed every morning, you can choose the size and number of pillows you have based on the size of your bed.
A twin bed looks great with a king pillow that covers the width of the bed with one or two accent pillows.
A full size bed welcomes two standard size pillows, two standard size or Euro shams, with one or two accent pillows.
Queen size beds hold two queen pillows, two queen shams, and three accent pillows. You can also replace the accent pillows with a single bolster if you prefer.
King beds hold three standard pillows and two king shams, with three standard pillows or three Euro shams, and three smaller accent pillows.
For a more plush look, really load it up with fluffy pillows that make it more welcoming.
However, you can overdo it, so make sure that your pillows span the width of your bed, but make sure they're between one quarter and one third of the length.
While this is largely a personal choice, this buying guide should help you determine what types of bedding are best for you based on climate, decor, and budget. There's no wrong answer, as long as you're sure you're going to love it.