I found I really love this hero, mainly due to being able to deal the most hero damage, most siege damage, most XP gained AND die the least even without an escape move or blink on 70%+ games.

you have to be clever about the zombies - trap enemies, possibly together with one of your own tanks or assassines, throw spiders into the pit, watch them die within seconds. always remember you can cancel the zombie wall with the W key if you try to help one of your guys to escape and he stops to throw another ability, ending up within the zombies instead!

don't hesitate to throw your skills as often as you like, you will hardly run out of mana past the earlygame where you can drink from the fountain - and all basic abilities are nice to damage minions and destroy walls. especially the toads are nice to get lots of poison onto an entire creep wave, granting you the death ritual benefit. at the start of the game, you should try to stay on the lane and gather many stacks of death ritual. you'll find that you're hard to kill later on, not an arthas or muradin, but still quite sturdy. which means you won't need an escape move like sprint if you play it smart and gtfo if things go bad for the frontliners. remember to call for retreat, throw zombies, THEN leg it. while running, you can still toss frogs and spiders and zombies and huge weird undead earth spirits over your shoulder to entertain your pursuer.

speaking of summoning half a supernatural zoo, towers shoot on ANY kind of non-heroic target first. which means your zombies and especially the ultimate are perfect to push in towers and even distract some fire from a minion wave so it'll last longer.