This is my downfall too. I may kill a lot, but I get killed a lot. Maybe this is why I'm always stuck in B rank.
Dying a lot isn't necessarily an indicator of low skill (although it would always be nice to avoid dying). If you are dying because you are going in deep and getting stuff done the death don't really matter. Dying is only a problem because you lose special and are off the map for a period of time. If you make each death count enough that the enemy won't have been able to undo the damage you caused by the time you get back into the fray all you have to worry about is losing special, which is much easier to deal with. Just make sure that you're always trading your life for something more valuable. A good list of things that are often worth dying for:
* Resetting the timer in Splat Zones.
* An even trade with a dangerous enemy (either very skilled or has a powerful special) BUT ONLY WHILE YOU ARE IN CONTROL AND HAVE A MANPOWER ADVANTAGE.
* Killing 2 or more enemies who are actually doing something, getting a kill on that guy who you've killed 6 times before is pretty meaningless. This is a good trade almost any time (assuming it leaves your team at a manpower advantage).
* Wasting a large amount of enemy time or special. A good example would be getting a Kraken to chase you all the way back to his spawn and use up all his special duration.
* Driving the enemy out of a heavily fortified position. You don't even need to kill anyone yourself (you really should get at least one kill though), you just need to break their lines and let your team get through. Example of this is using Kraken to chase enemies away from the choke point in Underpass and letting your team go through to actually contest the point.