Incentive or penalty ?

From a game design point of view, I think that hint cards break the magic circle. But the idea is sound, I would just change the representation to something that could be found in your game: battle plans, holographic training sites, commander logs, or something that fits into the world without breaking away from the game.

As far as teaching the player, the levels should be crafted to slowly introduce new tactical ideas into the player's bag of tricks.

to help the player i have these "collectable hint cards", which you find in the world, and which not only tell you how to set up an ambush (for example) using the game specific rules, but will also automate the actions for the player.

That's quite smart.

I 'm not sure how many hint-cards your game has, but assuming they all have different hints i would just give a small bonus on first-time use of any hint-card.

Dead Rising has "cards" for weapon recipes. You can built the thing without them if you know how, but the card helps you be more effective at it. It works well as a buff to a weapon, but I'm not so sure it would work for tactical deployment of troops.

The benefit would be the ability to quickly set up a formation or maneuver, and the penalty would be that the units will be blocked out in a way that might be less than optimal for the specific scenario. If you want your heavy gunner or your AT guy or whatever in a specific spot, and then when you play the "card" you get them distributed correctly, but sub-optimally, then you still have to tweak it a bit. Using the cards as shorthand for roughing out your troop placement would be a handy mechanic for quick and dirty deployments, but won't totally obviate the need for battlefield awareness and micromanagement of resources.

I would keep the cards as is and make sure the game is hard.

This would force the player into exploring the game mechanics, but if they can't overcome a specific encounter, then they risk discovering a new way to manipulate mechanics.

That way, they won't feel penalized for discovering it on their own.

Might even actually attach a cost when using the hint cards (but that may be a turn off).

I was thinking, maybe i should dig deeper into CCG mechanics, and make each "hint card" only usable once per combat encounter ? That will suggest to the player that variety is the only way, instead of repeating the same trick over and over.

I think it really depends on how the tactics are implemented. Take the cross-fire for example, if you put your units in the cross-fire formation without using the hint card can the game recognize the formation and provide a bonus.. or is using the hint card required to "trigger" a buff/debuff? If the hint card is required as a trigger then obviously it needs to provide a bonus, else there would be no reason to use it or the crossfire formation at all.

In either case, the hint card shouldn't really be a consumable... find it once and you can use it whenever you want, it represents knowledge, not a resource.

Well, that is a question...if i have a set of rules and values that describe a situation within the game, should i make it so that the game also recognizes that situation ? Basically there is really no point for the game to detect "this is a crossfire", the maneuver is supposed to simply work based on the scripting of the enemy reaction.

From a game design point of view, I think that hint cards break the magic circle. But the idea is sound, I would just change the representation to something that could be found in your game: battle plans, holographic training sites, commander logs, or something that fits into the world without breaking away from the game.

+1
For anyone who doesn't know what the "Magic Circle" is, this video helps describe it. "Hint cards" might not fit in well with the theme of the game, and break immersion.

I'm not sure how many hint-cards your game has, but assuming they all have different hints i would just give a small bonus on first-time use of any hint-card.

This is what I'd suggest; the first time you use your found Battle Plan, it gives you the 10% exp bonus. Every additional time, it doesn't give you any bonus, but you can still view it later if you need a refresher.

By "view it later", I'd intentionally put it behind two or three clicks of a menu (after the first use), so it's actually faster for a player to set up their own ambush rather than instantly pulling out the cheat-sheet for it.

There may be times when you don't want the game to automatically place your troops (after all, the player may have a particular reason they want to keep the positions of their individual troops situated as they are at the time). A player (like me) that wants the Battle Plans to be used not as an auto-attack tool (as that can take away from the engagement generated from the thought-process involved in planning an attack), but as an assist tool may prefer to simply have the types of movements highlighted for them, but completely optional, that way, if they want to fulfill the requirements for the "hint" task, but simultaneously want to fine-tune it to their own preferences, then they would be able to without have to just hope the computer would do it for them the way they want it.