Writs are city guild/quests that are usually given by people in the Fighter/priest/or guards area of the city //talk to everyone in Neriak with a quest feather above their head and you will find some, Good luck.
There are multiple tier's for writs, if you are doing adventure writs. You can follow This link, or This one.
Also, in the tradeskill area you can crafting 'writs' or 'rush orders'. Writs dont give you as much reward, but have no time limit, Rush Orders are timed and worth more status and coin.