How can I install a mantel?

Could you please elaborate on the steps required to install a mantel? I'm interested in understanding the process from start to finish. Do I need any special tools or materials? Should I measure the fireplace dimensions beforehand? Also, could you provide some tips on how to ensure a secure and level installation? Additionally, I'm wondering if there are any common mistakes I should avoid during the installation process. Finally, do you have any recommendations for mantel styles or materials that are suitable for my fireplace? Thank you for your help!