Any good resources for GM tactics?

Usually, attacking 3 times is a pretty good option for monsters, since they have such inflated attack bonuses. It is really good to model good tactics for your players if you remember to, though. (I usually forget to do this.)

For more intelligent monsters, have them step back out of melee range with their 3rd action, or open with a Grab, Trip, or Demoralize. Those are actions any monster with the skill can take.

Generally if a monster has a unique action, you should use it as soon as applicable (even if it's not technically the best action to take). Monsters have limited screen time, so make sure to showcase the unique things they can do!

Monsters can use skills too, so look at what skills they have and what basic/trained actions they have access to. Disarm is a joke until an enemy disarma the fighter and then attacks their sword, destroying it (since it's an unattended object). Also, your players might hate you if you do that.

Move around, if you are going to make a 3rd strike it's probably better to move away unless the player has an Attack of Opportunity or similar, and even then you can just step away.

Use terrain more. The mosters are usually on the defensive in my games, so they might have traps, advantageous terrain, etc. If the enemies are shooting from a balcony then they are not in melee range, and probably can Take Cover each round. If the usually melee PCs made the mistake of not carrying a ranged weapon they'll need to either find the stair up or climb which is not ideal.

Use (magical/alchemical) items! There's quite a long list of them and I feel they are underused in the game, my players at least have this "I might need it later" mentality, specially (but not only!) towards consumables. I personally blame Final Fantasy for that, oh well.

Basically any advice that works for the PCs is going to work for the enemies tactics-wise.

My two cents: The step reaction, is an action in and out of itself; so you could chain multiple steps to keep goblins moving together.

Alternatively; lets imagine a goblin beside a Barbarian; in a grid (G for goblin, B for Barbarian)

Goblin1 is to the left of the barbarian. Goblin 2, comes from lower, coming right to the barbarian; it strides or steps into range, and ends just below the barbarian; within 5 feet of goblin 1 Goblin 1 can then use its scurry reaction to step; and it moves diagonally to the square over the barbarian. Now, Goblin 1 and goblin 2 are flanking Barbarian; Goblin 2 can now make an attack with better chance of damage.

Funny thing; since the reaction can trigger another action (i believe so, but i may be wrong) you could have a line of warrior goblins; all stepping "at the same time" by reacting to the nearest ally stepping. Or a group of four goblins together, one steps outward; they can all follow by chain, or go in different directions.

The cool thing about the scurry is that they can pretty much dance around a pc; it can be offensive or defensive, but is not as much movement as the kobold retreat

Kobolds, as long as there's some frontline, could go like this: PC is fighting some frontline that can take hits Kobold strides into pc's range, making sure to flank Kobold attacks, which trigger their sneak attack extra damage to flat footed targets Kobold uses hurried retreat. It's hit and run, but if there's a bunch of kobolds, and they can get cover behind some terrain(which they 100% SHOULD DO, they should attack somewhere they can take cover behind large rocks, small cave passages etc)

And in general, a lot of tips on strategy are relevant throughout many TTRPGs and Wargames, almost universally; Due to this, you can almost always extrapolate tactics from somewhere like " https://www.themonstersknow.com/ ", which is quite a good source for inspiration imo

I don't know of any resources, but what I do is using skill actions. Athletics, Deception and Intimidation are what you'll be mainly looking for because Athletics has a lot of fun stuff on it, Intimidation is Demoralize and Deception is Feint.

But never attack thrice, moving away is better even for meele and unintelligent monsters. If you look into animal fights videos you'll see that, unless they're grappling, they always do the back down-charge!!-back down-charge!! cycle as well. Even lions hunting larger prey do that.

Intelligent monsters will act intelligently and go after the most immediate threats to their safety first , they will be worried about the archers and mages in the back line , and they will try to coordinate their group to keep the melee enemies engaged with their melee units while their ranged units attack their enemies ranged units. Or they will use ambushes to deal with these threats first.

Animal monsters will simply engage the closest enemy and attack and retreat if they are injured.

He get some fun in encounter by using Demoralize and combat maneuver. Players always fear when I roll for a grapple or a shove to make them flat-footed between two monster.