Well early on in the Wraith Night event I recorded some stuff with some early tips. Its been on youtube for a while but I thought I'd share it here too. Theres some tips to not screw up early on. I really wish they would make events like this permanent additions as a mini game mode.
I split it into the 3 games I played. I would recommend playing with a team for this, sometimes getting paired with someone who refuses to play as a team can be a real problem and will usually kill you off before wave 5
As far as a team goes you need a ranged character, a good tank, and someone to heal or prevent damage. Otherwise just have fun with it as it really depends on which wave you are on as to which character is best. I find a certain two headed dragon to be very useful in the early waves because of his amazing AOE. Legion commander is good when you start getting bigger enemies because of the lifesteal you get from her ult can help you take someone down AND heal. Omni Knight is very useful as he can basically make your tank immortal until he runs out of mana, just need to make sure you have a good tank who realises keeping Omni alive is very important.