Arduino RFID Library for MFRC522 (13.56 Mhz)

Pin order, starting from the bottom left hand pin (in case your MFRC522 doesn't have pin markings like the B2CQSHOP one):

Pins	SPI	UNO	Mega2560	Leonardo/Due
1	SDA (SS)	10	53	10
2	SCK	13	52	SCK1
3	MOSI	11	51	MOSI1
4	MISO	12	50	MISO1
5	IRQ	*	*	*
6	GND	GND	GND	GND
7	RST	5	?	Reset
8	+3.3V	3V3	3V3	3.3V
* Not needed
1 on ICPS header

Using MFRC522 with other SPI components

If you are planning to use other SPI components you just have to make sure each have an exclusive SS (Slave Select) line. MISO, MOSI and SCK lines may be shared. More reference regarding SPI may be found here.