A major difference in strategy with Fourthcore Team Death, as opposed to standard 4E D&D, is mathematics behind combat. In standard 4E D&D, enemies (ie. monsters) have a certain limited range of defenses. In FTDM, however, that assumption is thrown out of the window completely.
The 1st Level characters that FTDM requires, by and large, have at least one easy-to-hit weak point in their defenses. Very few enemies you will be seeing at these events has their lowest non-AC defense much higher than 12, and sometimes far lower.
So, when building your deathmatch dungeoneer, a common strategy is to have a variety of attacks that target different defenses, and to always go after the low defenses on the table. Defenses must all be displayed publicly during a match, so it is just a matter of vigilance and cunning to exploit your enemies' weaknesses.
A Trick Up Your Sleeve
When choosing at-will and encounter attack powers, keep an eye out for attacks that confer useful situational bonuses that can be exploited for different contingencies. A great example of this would be an attack power that can be used as a basic attack when your dungeoneer doesn't otherwise have strong basic attacks. Your encounter powers get recharged very often via the Respawn mechanic, typically about every other round, so don't always assume that it is a better choice than using an at-will attack.
Read the Maps, Use the Terrain
Just as simple as that, the most important thing you can do to prepare for a FTDM match is to read the map and understand how it functions. Using map powers to your advantage can rack up many kills without ever having to dip into your own attacks. Each map has its own unique features, be sure to understand them well.
Lastly, don't forget to choose a Background. Though some special boons, such as Themes, are disallowed in FTDM; non-Forgotten Realms Backgrounds are still FTDM-legal. Unless the maps you are playing on dictate otherwise, look for Backgrounds to enhance either your Athletics or Acrobatics checks.