Turn it around
=
Players shouldn't state the skill they want to use for a given situation, they should state their intentions. As the Game Master, **you** know how that intended action can be adjucated, and you will request the player to make a Perception / Diplomacy / Bluff / Whatever skill check.

Instead of the player saying
> I want to roll a Perception Check to look around the room.
>
> I want to roll a Diplomacy Check to tell the guard to calm down.
>
> I want to roll a Stealth Check to sneak past the sentry with these clothes I found.

You should teach them to describe their intentions and approaches
> I look around the room. What do I see?
>
> I want to unsheathe my sword and tell the guard to calm down.
>
> I want to use the clothes I found to sneak past the sentry.

Upon which you might (or not!) request the player to roll for a check. Remember that it is up to you to determine if a result should be randomly determined. If an action as described is simply impossible, or extremely hard, don't make them roll! Rolls without a true purpose only bog down on the pace of the game.
> You see a mural that depicts the battle of your ancestors. [You roll Perception Check behind screen, succeeds] You also see a key lodged between two bricks in the wall.
>
> You pull out your sword and tell off the guard. Roll for an Intimidate Check.
>
> You put on the clothes you found in an attempt to blend in with the crowd. Roll a Disguise Check.

Players are focused on what they are good at
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Note how in the last two examples, you asked the player to roll a different skill than what I described in the very first example block. Players often look at their character sheets, find a skill that is highly trained and try to use that over something else. They might try to use Acrobatics instead of Climb, or Intimidate instead of Bluff. Make it a rule of thumb that they are not allowed to ask for skill checks. Only let them state intentions or ask you questions about the in-game world. And you can (or not!) ask them for a skill check.

The [Angry DM has a very good article on adjucating actions](http://angrydm.com/2013/04/adjudicate-actions-like-a-boss/). It has helped me with a situation like this.