Eye in the Sky...
This may sound a little strange, but usually in combat, I play kind of the "eye in the sky" - I'm usually out of the combat entirely, playing "field general" and directing the other characters in tactics; where to go, what to watch for, etc. I may put in a "Front Line" appearance or give ranged/magical support where necessary to help us win, but most often my character is well removed from the action and giving tactical advice to his companions.
It may be a very weird choice, but in general, the groups I am with have found that they tend to be much better able to survive with me as an "eye in the sky" giving them orders that may not make sense individually, given their position, but help the tide of the overall battle, as seen by one not actually mixed up in the action. It usually only takes a couple of gaming sessions before a group trusts my intuition (in D&D I usually play high-Int, high-Wis spellcasters with access to communications spells and/or the odd long-range blast spell; in high-tech stuff, I'm the dude barking orders in the radio).
Can't describe it quickly any better than that, but I've found that having a field general/tactical commander who DOESN'T take part in the fighting on a personal basis very often tends to drastically enhance a group's survivability.
--The Sigil