I have to say i'm pretty much a rambo in many respects. I try to organise pub teams sometimes and sometimes it works but often it doesn't.
As far as fighting I take the approach of "kill the enemy in the fastest way possible".
Whether that's attacking unprotected/unaware backs, gang banging, flanking etc.
I'm at my happiest when an opponent drops his weapon and doesn't try to block so I can kill them quickly.
Knowing when a fight is going to take a long time is when you break off and attack others, and then hope to catch the original opponent unaware, some seconds later.
If an enemy is attacking a team mate close to you, attack them just before they go for your team mate and you should get a hit in.
If you're 2v1 then use a different attack direction to your team mate. If they're using a spear/shield then you can guarantee they are going for a stab, so you can choose any of the other 3.
In public siege, most players will go for a right swing attack, and following on from that most players will switch to right swing block as soon as they've attacked. You can counter this by not always using right swing attack