This has come up before and I saved my notes on it. It is not animal specific but assumes that creatures with feats, special abilities, or special qualities know how to use them correctly, if not inventively. So this infers tactics from D&D stat blocks and combines it with the most fundamental maneuvers that virtually all creatures use.
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The encounter should have a purpose and the simpler you keep it the better: "get food", "protect young", "defend territory", "take shiny thing," etc. Most of these will result in the creature fleeing if they take any noticeable amount of damage. Dead things don't breed so genetics favors discretion.
Everything with an Int score is bright enough to target the smallest/weakest creatures first. The exception are territorial animals, who may charge the largest member of the invading "pack" to establish dominance. Weakest may include creatures moving slowly, appear to be crippled/smell of blood, or that show signs of being diseased/poisoned (scent is a handy ability). Typically, only brainless monsters like insects grab the first creature to approach.
Attacks are made on the rear and preferrably along the line of travel. This keeps attention focused away from the attacker until too late and provides some degree of cover due to the intervening creatures.
Creatures that naturally occur in groups will use basic pack tactics, which boil down to "dogpile on one guy until he stops moving, lather, rinse, repeat." The eternal goal is to cut down the number of foes as fast as possible. With raw damage that means focusing on one creature. Conversely with attacks that can incapacitate foes regardless of health (poison, stun, etc) you want to hit as many people as possible.
Look at the Special Attack/Special Qualities/Feats lines. These are the tricks and unusual maneuvers that make the creature something other than a wall of meat. If those lines are blank then hey, wall of meat. Crush, kill, destroy.
My personal standards are:
Regen/Fast heal: these creatures use hit & run tactics. You can afford to bleed people to death if you heal ten times faster than they do. IMC trolls make their attacks and if they start taking any significant damage, they retreat, wait 2-3 minutes (20-30 rounds) and do it again. If their foes appear to fast heal as well (aka "cleric") they may give up but with a high enough Int (8+) they will be able to tell the difference between natural fast healing and magic and will try to overwhelm the cleric's healing ability.
Damage reduction: tend to be highly confident since they ignore many creatures' attacks. Things with very high DR may use incredibly unconventional tactics, like an ambush involving a leap from a cliff. (1d6/10' fall = 3.5 hp/10'. DR10=30' drop. Helloooo drop-bear.)
Improved grab: the creature will understand the strength & weakness of grappling. They will likely go for the smallest, easily trounced foes to minimize the time they lose their dex bonus.
Improved trip: are not stupid enough to trip things significantly larger than themselves. They will gleefully try to trip things smaller than them or that are the same size with fewer legs. Much like stun & poison, trip as many creatures as you can since it cuts down their number of attacks without reducing your own damage output.
Pounce: the opponent can attack from a fairly great distance and still do a sizeable amount of damage. The creature will likely retreat to evaluate success. After all, the dead thing will still be there when the others leave. And wounded creatures are easy to track.
Rend: creatures with rend tend to avoid power attacking the first round or two to ensure they land enough hits to pull off a rend. Renders will try to trap their foe so they don't have to worry about chasing them down.
Stun, Poison, Fear: the preferred opening salvo, soon and often. As many different creatures as possible should be targeted to incapacitate the maximum number of foes. In the case of stun, attackers should try to position themselves so that they can try to stun a foe with one attack and have the option of using their other attacks on allies' stunned foe. If a creature shows no particular reaction to being poisoned, the attacks should shift to one that is. Area effects should be overlapped if possible to increase the odds of failed saves.
Blindsight/sense: These creatures work best in pitch black or, even better, inclement weather like fog or snow that eliminates darkvision. Sentient creatures will try to arrange those conditions, possibly by using smokesticks or just building a smoky fire. Blindsight/sense is also functional in very dense jungles where anything more than 3' away has total concealment.
Charm: creatures who can charm should do so before launching any attack, attempting to charm the entire group. They should present themselves at a distance to evaluate the effectiveness of the charm. They should approach the charmed ones in as peaceful a manner possible and attempt to maneuver one away from the others. Intelligent creatures should attempt to sow confusion, and if sufficiently cunning, convince an uncharmed creature to make the first attack.
Darkvision: prefers the night or underground where their senses give them an advantage.
Death attacks: target the scrawniest individuals first as they are least likely to make the save. You may get more "bang for your buck" by taking out the largest foe but the goal is to cut the numbers down quickly. Furthermore, creatures with death attack should milk it for all it's worth, attacking from ambushes and breaking off combat at the first sign they are not winning. In this case, quantity does have its own quality.
Disease: creatures with the disease ability should attack as many foes as quickly as possible and retreat so they can stalk the group for the next few days where they can continue trying to infect the healthy and injure the weak. Attacking while the sick/injured are sleeping is best, even if doing no damage, as interrupting sleep prevents healing.
Energy drain: has the advantage of healing the user. Typically it should be used to eliminate foes quickly but given the lack of a save it may actually be worthwhile to use on the strongest individuals. This tactic should be used when only one or two foes have attacks that are effective.
Etherealness: excellent for surveillance and stalking. An ethereal creature may take days to survey their victims and learn their habits.
Gaze attacks: creature prefers to function in full daylight, unless they have the unusual quality that their eyes glow. (Yes, I am that evil) Creatures with gaze are fairly bold and forgo stealth. They may however use subterfuge, mimicking other creatures' noises to attract victims. Creatures with gaze like open forests or cave systems where they can take advantage of the range of their gaze but with enough concealment that their foes are unlikely to identify them at distance and avoid them.
Invisibility: any creature than can be invisible should be invisible. Period. The world is a harsh and dangerous place. Only creatures that have a limited usage of invisibility should husband their invisibility. Invisibility should be the first action, preferrably followed by movement as long as it doesn't risk AoOs. Creatures with invisibility should also attempt to attack at range from concealment so they may become invisible again without being found.
Paralysis & hold: like stun, use it early, often and on as many opponents as feasible. If a creature appears immune, avoid/ignore it to eliminate other foes.
Trample: like pounce but better since it can be used on multiple foes. A trampler can attack from a moderate distance and race away when done. Tramples do NOT have to be in a straight line by the SRD so it can be selective. The goal of a trampler is to pulp one specific individual and catch as many more as possible. A smart trampler will avoid focusing on someone with evasion; remember the eternal goal is to eliminate as many foes as quickly as you can. Trampling does not need to hit AC so it can be used on otherwise unhittable targets. Furthermore, if you are careful in your path you can keep your foes too busy dodging (making reflex saves) to make their AoOs on you.