SPI and the DHT11 Sensor
Adafruit's tutorial/datasheet for this sensor is an easy read. The device's voltage range range is 3.3V to 6V. A 100nF capacitor can be placed across VDD and GND for stability.
The DHT22 datasheet is more complete so it is also included since the only real difference between the two is temperature range.
Wait for 1s after powering the DHT11 before communicating with it. Wait 5ms between communications.