This is going to annoy a few people (because some people just plain and simple hate this notation), but my favourite way is ~(1<<n) -> Probably because I first learnt C on the AVR microcontroller, and that is the method for writing to registers.
This clears the bit SPI2X in the register SPSR.
Or you can see how a full register can be set up
SPSR &= ~(1 << SPI2X); /* No doubled clock frequency */
/* initialize SPI with lowest frequency; max. 400kHz during identification mode of card */
SPCR = (0 << SPIE) | /* SPI Interrupt Enable */
(1 << SPE) | /* SPI Enable */
(0 << DORD) | /* Data Order: MSB first */
(1 << MSTR) | /* Master mode */
(0 << CPOL) | /* Clock Polarity: SCK low when idle */
(0 << CPHA) | /* Clock Phase: sample on rising SCK edge */
(1 << SPR1) | /* Clock Frequency: f_OSC / 128 */
(1 << SPR0);