Kel'Thuzad the Lich a quick guide
March 6, 2012
There are two most common ways to play Lich - the solo mid and the support style. Solo Lich focuses on keeping the opposing solo down by harassing agressively and using Dark Ritual to deny XP and keep creeps near his tower. Support Lich abuses his item and mana independance to give the most to his team.
Remember that if you skill Ritual first, you can deny almost half of the first creepwave.
Frost Armor is particularly good against enemy melee carries - getting an early level of it may be a good idea in this case.
You ultimate works best when there are 2-3 enemies clustered together. However don't be too picky waiting for the "perfect moment".