How to Get Good Legendaries: A Guide to WoW Excellence by Fundie

Step 1) View all your class / spec legendaries in the Adventure Guide
Step 2) Concentrate on the one you want. Prayer works too*.
Step 3) Kill Warlord Parjesh on normal Mythic mode and almost neglect to loot him.
Step 4) There you have it, your very own good legendary.

If you did not receive your legendary after following this guide, you are either doing it wrong or WoW excellence has evade bugged you.

*Also helps if you are white.