Adventure authors don't speak to players directly; the communications are filtered by the GM at the table. There are some obvious exceptions to this, such as boxed text meant to be read aloud to set a scene, but there are some secret ways an author can communicate tactics to savvy players. It's sort of like a hidden language. Much of it rests in how the adventure describes the enemies the players face.

An enemy's appearance doesn't just convey the likely threat (and armored hulk with a huge sword is going to do a lot of melee damage, for example). It also conveys likely weaknesses, and experienced players can pick up on these. Some examples:

A foe described as nimble and wiry, like a sneaky rogue, will have great Reflex/Dexterity saves, might have good Fortitude/Constitution saves, and is likely to have terrible Will/Wisdom saves. The foe will have a high AC but not a lot of hit points. This description says "use enchantment or illusion spells" and "landing a hit will be tough, but you don't have to land very many to knock this foe down."

A foe described as a scholarly wizard, particularly one that casts spells that seem just a bit more powerful than the party could cast, will have great Will/Wisdom saves, might have good Reflex/Dexterity saves, and is likely to have terrible Fortitude/Constitution saves. The foe won't have a great AC or very many hit points, but could have a lot of surprising magical defenses. This description says "don't count on spells much, but ones that petrify or paralyze will work best" and "melee is where I'm weak, so close in to attack. Prevent me from casting spells." For the properly prepared and morally flexible party, it also says, "poison me."

A foe described as a muscled, armored warrior or a giant, will have great Fortitude/Constitution saves, but probably has terrible Reflex/Dexterity saves and Will/Wisdom saves. The foe might or might not have great AC but will have a lot of hit points. This description says "cast spells on me for greatest effect" and "meeting me in melee is to fight on my terms, and you'll do poorly; remain at a distance." 

A priestly foe--that is, one with a prominent unholy symbol or encountered within an evil temple or shrine--will have a great Will/Wisdom save, a good Fortitude/Constitution save, and a terrible Reflex/Dexterity save. This foe will have a surprisingly good AC, particularly if given even a few rounds to prepare, and a moderate amount of hit points. This description usually says "fireball me."

Although an adventure author might occasionally subvert these appearances (a scholarly wizard-looking foe might actually be a monk, for example), it's best to rely on them most of the time. These appearances are like a language to players. Players like to feel like they're employing good strategy, so rewarding them for relying on a description is fun for them. When a foe's apparent weakness turns out to be a strength, it teaches players that they can't rely on enemy descriptions to guide their tactics any longer, and that eliminates one of the ways PCs listen to GMs. A piece of the language is lost.

Note that these appearances virtually never apply to PCs, because they learn their own weaknesses over and over and delight in shoring them up with clever character builds. That's fine; the monk PC who dresses in a wizard's robe and pointy hat to lure melee foes close, and the priestly PC who prioritizes Reflex/Dexterity saves, are all speaking the same language; they're just trying to fool their enemies with that language. A GM should have foes "fall" for this from time to time to make the PCs feel clever, and adventure authors can help with this. A giant who attacks "the PC that most looks like a wizard" or a demon who casts fireball centered on "any PC wearing a holy symbol" lean into this.