With regards CWS' and Gabe's points, in a military style contact the visible enemy is not likely to be firing he will be moving and will be covered by his buddy this is the basic principle of pairs fire and manouevre "one foot on the ground"
As a guideline during this type of training the guy moving would repeat the mantra "I'm up he sees me, he sees me Im down" which takes under 3 secs, immediately on going to ground he would once again crawl laterally then open fire to cover his buddy who repeated the procedure, prior to the next bound the cover man would shift position again so he did not get up from where he'd been firing from.
These tactics were for advancing on an enemy position after taking fire and would also be covered by the section support weapon which would deploy to put down suppressive fire on the enemy position from a flank.
In a rural environment it is unlikely that an enemy would "pop up and shoot" as they would normally be in concealed position covering their arcs and then merely open fire once the approaching targets were in their kill zone. However in an urban environment there may well be situations where hostiles "pop up" from round a corner etc and open fire as is seen a lot in Iraq! Bearing in mind that such tactics will not allow the hostile to put down aimed fire initially, good patrol skills may well enable us to take out the hostile without drastic movement.
To translate this to a possible civilian type encounter obviously depends on a variety of factors firstly are you alone or do you have a buddy that can cover your movement? then in what type of terrain are you operating and what is your "mission"?
So in essence we need to train all 3 of Gabe's options
1 - for when we are moving through an urban / CQB environment and a tgt appears in our sights
2 - as CWS pointed out if a good tactical postion is immediately available and moving would expose us to fire and we have located the enemy
3 - In a rural environment or a longer range urban environment where the enemy is not immediately visible.
There is one other tactic that has not been mentioned that of anti-ambush where the ONLY option may be to assault straight at the enemy position while firing, as that is usually the only way out of the killing zone of a prepared ambush (if your still alive) as any infantry man will tell you!
hope this adds some more food for thought :)
...If you can force your heart and nerve and sinew
To serve your turn long after they are gone,
And so hold on when there is nothing in you
Except the Will which says to them: "Hold on!"...
If - Rudyard Kipling
ECRG, June 2006
Warrior Skills Camp, July 2009