Make sure you have a good & reliable SD card and a proper power supply. Archives can be uncompressed with 7-Zip on Windows, Keka on OS X and 7z on Linux (apt-get install p7zip-full). RAW images can be written with Etcher (all OS). Where images are compressed with .xz you can wrtite them to the SD card with Etcher directly.
Insert the SD card into the slot, connect a cable to your network if possible or a display and power your board. (First) boot (with DHCP) takes up to 35 seconds with a class 10 SD Card.
Log in as: root Password: 1234. Then you are prompted to change this password (US-Keyboard setting). When done, you are asked to create a normal user-account for your everyday tasks.
* Specifications differ from hardware revision, model and software support level