For Level 52 Death, most of your early opponents will be between Levels 40 and 65. It is crucial that you find a hat, robe, boots, ring, and athame that will give you resist, Death hit boosts, and critical block. The Glendemming set is what you want to aim for when you get enough tickets.
Your deck planning is also important. Make sure you have learned the following spells before you make a deck:
Ice spells up to Tower Shield
Balance up to Weakness
Sun spells up to Giant
Life up to Legend Shield
Fire up to Glacial Shield
and, if you can learn Deer Knight from Loremaster or Knight's Lore Pack, do it
Try the following in your deck:
Max Tower Shields
2 Spirit Blades
3 Doom & Glooms
whatever else you want
Make sure you pack at least 1x of the following Treasure Cards:
35% Time of Legend or White Rat Magician (to clear opponent bubbles)
55% Tower Shield
Monstrous-enchanted hit spells (mainly Poison and Wraith)
Some final notes:
DO NOT simply blade, blade, hit with your biggest card. That strategy is easy to thwart. Try defending yourself, saving your pips, then using Infallible and unleash a poison-poison-vampire combo.
Defeat minions with Banshee or Vampire. (Unless you have Deer Knight.)
Practice messing up your opponents' hits. A lot of private-veteran ranked wizards think they can beat you with one big hit. Beat those hits, and you are half-way to a win.