Where do you lane him/ what role?
Anywhere but jungle: mostly dual offlane, once dual mid, a few times safelane with a support.
I got a first blood once by spamming wraith at the 0:00 rune with the help of a Pudge. Otherwise, I just level up Q and stats, and spam Q on lone heroes in lanes. The harass on the hero with the lowest regen is ultra strong.
From my point of view with normal skill bracket everyone who picks him is absolutely terrible. Arc warden is definitely a good hero, just not in my bracket.
Do not feed necros. Push lanes and jungle constantly. Always help team with magnetic field once you get travels 2. Build any item that has an active that you can use: blink, abyssal, diffusal, maybe atos, etc. Otherwise, just build whatever is expensive, but do not feed rapiers.
Watch this for solo offlane versus Gyro:
http://www.dotabuff.com/matches/2029277566
Watch this for afk jungle-push:
http://www.dotabuff.com/matches/2029333925
Watch this for an epic comeback:
http://www.dotabuff.com/matches/2019691866
Against certain drafts, you know you will eventually win. Against others, if people are decent, they will manage to keep all the lanes pushed all the time and you will have a hard time.
The good thing about jungling necros is that you occasionally deward the map!