Lian is a champion capable of dealing medium amounts of damage over short periods with her abilities, all of which are capable of dealing damage. She is best stationed in the backline dealing damage from medium distances or even long range with Presence. Moreover, her ultimate, Enlightenment, deals 1600 damage and fires in a straight line, making it optimal for applying a high burst of damage against flanks as a last resort or hitting a large group of enemies bunched together at the same time. It also grants CC immunity and reduces damage taken. Additionally, she is unique in that all of her abilities apply on-hit effects like Cauterize.
The talent I generally prefer to use is Eminence due to the high damage you can deal while at far distances, making it an ideal method of hitting enemies no matter how far away. Her other two talents, Alacrity and Precision, can also be useful, but Eminence is better, as the loadout card Heraldry enables you to theoretically use it multiple times in a row.
Although items are subject to each player's preference, and some items like Bulldozer and Illuminate may or may not need to be bought, I generally use Cauterize and Haven as my two main items.
Present Arms is not mandatory to have, but having the extra healing can be nice, seeing as Presence can be used multiple times if you hit at least 2 enemies at once. However, it can be replaced with Manifest Destiny or another card if you want.
Increase the damage of Presence by up to 50% based on the range at which it hits and reduce its Cooldown by 4s.
Hitting an enemy with Presence reduces its Cooldown by 5s.
Heal for 200 after using Presence.
Reduce the Cooldown of Presence by 1.2000000000000002s for each enemy hit by Valor.
Reduce your active Cooldowns by 40% after earning an Elimination.
Increase your maximum Health by 100.