What type of HDMI cable is recommended for this TV, and are there any connection warnings?

LG recommends using an Ultra High Speed HDMI certified cable of 3 metres or less. You must use a certified cable with the HDMI logo attached — if you do not use a certified HDMI cable, the screen may not display or a connection error may occur. Also, both the TV and the external device should be turned off and unplugged before connecting the HDMI cable. (Page 6)