Death is part of dueling. This sport is dangerous! But there are things that a manager can do to help keep his warriors alive. Nothing is a sure thing, and a warrior with maximum hit points (21 con/siz/will) can still die. There is some luck involved regardless, and luck can run both ways. But here are the experiences of Assur with keeping warriors alive.
1) WIN! It is impossible to die unless you lose a fight. In fact, some of the suggestions later on may hinder your ability to win somewhat, so this should be the first and highest priority in keeping your warriors alive.
2) Wear armor. Any armor. Especially a helm. It is Assur's experience that warriors with NO armor die way more often than warriors that wear armor. On the other side of that, Assur has no conclusive proof that APA gives any additional protection against death than ALE. It likely does, but the benefit from none to ALE is much greater than ALE to higher armors.
3) Lower your KD, especially in desperation. There are tons of theories about what different KD does, but nobody is completely sure. But Assur has found that is does change your ability to kill and be killed. Want to live? Go low, really low. Want to die? Go high, really high. Assur guesses that it changes your desire to keep fighting (both winning and losing) and the arenamaster respects that and lets the fight continue or ends it sooner.
4) Protect HE and/or BD. If it is a warrior that Assur really wants to live, he'll often protect one of these areas during minutes 1-6, and another in desperation.
5) Hit Points, especially Size and Will. Smaller warriors seems to die more often. It is also believed that Will is directly related to the stat that is checked when your warrior enters the infirmary.
6) Stay away from known killers. See that 3rd number in your opponent's record? It means something. If that number is anything greater than 0, it means your opponent has killed before. When that number is 2 or higher, it suggests that you may not want to fight that warrior (or if you do, make sure you win).
7) Look for managers that aren't killers. You will definitely see patterns over time. Divide kills by wins for a team's career record. That is a great indicator as to how bloodthirsty a manager is. .10 is a very high kill ratio. .05 is a manager who probably tries NOT to kill.
8) Stay away from huge mismatches. For whatever reason, it happens over and over again. Young upstart challenges or is matched against very old veteran. The end is an early demise for the arrogant young upstart.
9) Fight warriors that aren't going to kill. The opposite of 6, but this goes one further. Pure scum Total Parries that let a warrior run himself to exhaustion don't kill very often (since they don't attack very often). However, see the final item.
10) Stay out of exhaustion. Warriors seem to die much more often when they are completely exhausted. Your opponent starts hammering down the blows and your warrior takes blow after blow.
-- Assur