Je recopie ici l'une des interventions qui m'a le plus frappée. Peut-être ferais-je un petit résumé en français à l'avenir.
Epidiah has it, it's all about positioning: the default combat round is a melee where you just count everything together, but you can achieve quite a satisfying amount of tactical variety by positioning. Basically, you're splitting both forces up into an arbitrary, fiction-based number of subgroups, which are then matched together on the basis of fictional maneuvering. The basic goal here is to have everybody in your force fight a small subgroup of the opposing force while a majority of them twiddle their thumbs, run in confusion from point A to point B, are stunned or are otherwise occupied: force concentration in one place to cause defeat in detail for the opposition. You achieve this goal by inventive tactics in between melee rounds: each melee round depicts the span of time from the commencement of hostilities to a break in the action, so by definition you will be able to move, talk, cast spells, escape and do other things in between those melee rounds. If it has been established that some of the enemies are close by and some are farther away, attack quickly to get a melee round against only a portion of the force; if it's been established that the enemies are ready for action, withdraw and try to break them up, or use special weapons (molotov coctails are a perennial favourite in the genre) to break up the formations and sow confusion, all to get that tactically superior position. If all else fails, sacrifice a minor part of your force to attract the enemy to split, then defeat them in detail.
Another issue are multiple goals that come up in complex tactical situations: you might have to divert a part of your forces to fight on a complementary front or to do something else with a Saving Throw, or simply to cause some tactical effect you'll absolutely need to win the battle over the long term. Melee rounds always take time, so even the most cohesive force might lose the entire fight by being delayed and misled into excess force concentration, especially if you can get inside their decision-making loop by reducing and slowing down their information flow. In practice you do this sort of thing by avoiding the melee round (Saving Throws), and by sending only partial forces into them, and by limiting the decisiveness of the engagement (basically limit both yourself and the opponent to fighting with less than their full force). There are an infinite amount of stratagems, but a tactical withdrawal is both a complex and basic example: you draw a portion of the enemy force off in pursuit, position your own rearguard for ambush with Saving Throws, turn back to face the quickest enemy forces with your front for a turn, continue the escape, lead them into a trap, engage, disengage and so on, ideally whitling the enemy down by refusing engagement.
An important special case is force quality: where you have superior individual fighters, you might be able to use this tactically by encouraging limited confrontations instead of all-out melee. As always, the "everybody rolls" melee is your default position that you engage in only if the combat happens for no particular reason in a completely generic setting with no options for positioning. If, on the other hand, you're fighting knights and one of your own forces happens to be invulnerable and you also hold a chokepoint, it's sort of obvious that what you'll want to see is a series of duels the enemy can't refuse due to honor and tactical reasons, but which they also can't win because you have this one guy who can beat any one of theirs. The point is that the seemingly communal fighting system is only that if and when you allow the situation to become a generic melee. Duels can and will happen, as will ganging up on enemies.
Note that the combat system of the game works exactly as it should here: equally strong forces will likely not cause much harm to each other in one melee round, while an overwhelming force will typically crush the enemy immediately, which means that the value of time as a currency changes from situation to situation; one might say that the equal forces will fight more rounds because they will be able to disengage more often, while a routing, inferior enemy will be forced off the field before they have a chance to remaneuver. Distributing damage within the losing side comes in here as well: the rules text has the losers choose their own distribution, but I usually allow the fiction to inform here in the form of pre-round positioning and post-roll stunts and such. (In my experience this is automatic, players have more fun when they go "of course the fighter takes the damage, he's in front" rather than trying to optimize too much.) Regardless, the fight is only about grinding multiple melee rounds in a row when everybody's run out of ideas and the weaker party can't escape for some reason; in all other cases you absolutely want to use those moments between rounds of savage combat to reposition and try to gain advantage anew.
Speaking of stunts, I myself like to use Spite damage as a sort of stunt and special technique pool, especially for fighters. Want to disarm the opponent - roll a Spite point and spend it for that. Want to end your melee round behind the enemy force - spend Spite. Want to make a Saving Throw maneuver as well as fight this turn - spend Spite. This works better than pure Saving throws (especially the stupid "lose your melee round to make a Saving Throw" idea in the rules text) for some things, and remember - this is a refereed old school game, the presumption is that you'll use the subgames and mechanical conventions that you like and that flow in the moment. I personally happen to like having a bit of special crunchy sting in fights, so I expand the Spite damage concept the teeniest bit; monsters get to do special maneuvers fueled by Spite, too, so why not PCs.
Also, I have to say that I agree 100% with anybody who reads the text and thinks that the system is not explained clearly, and is not implemented very excitingly in the examples. I've no idea what's going on there, frankly; this is a very nuanced fantasy combat system with more realism (psychological and cinematic credibility, rather) than any Runequest derivative, so it's sort of a shame that it's not been written up very clearly. I don't know of a superior system for highlighting the nature of melee combat against the desperate breaks and breathing space combatants gain now and then. The mainstream (Runequest, later D&D) train of thought is all about sliced time, movement in melee and robotic precision in split-second decision-making, which is not at all what I want fantasy combat to be: I want insanely chaotic melee rounds with risk and implicit movement, intersped with tactical maneuvers. T&T delivers this beautifully, making it my number one choice when I want true-to-life archaic combat for a roleplaying game. The system being dead simple in its basics is a big bonus, but not my first reason for liking it.