cave quid dicis, quando, et cui.
*cracks knuckles*
First thing is first: Identify the main verb and the subject. The main verb is "Dicis" which is the second person singular, present active indicative form of (dico, dicere - to say, tell, speak.) That's a bunch of gibberish to sort through, but it all means it is translated as: You say/You are saying. Since there is no "subject" word in this sentence, or at least none of the ending indicate one, the second person pronoun "you" which is used when translating the "second person" verbs becomes the subject.
Next, let's work through this sentence left to right, starting with "cave." It's either an Ablative Singular form of the noun (cavus, cavi - hole) or it's the infinitive form of verb (caveo, cavere; to beware, avoid. ) The noun would be translated "By/with/from the hole" and the verb would be translated "To beware." We'll translated the rest of the sentence and then plug whichever translation makes the most sentence into its slot.
Moving on to "quid." If I remember correctly it is an indefinite pronoun that is translated as simply "what/why."
Next up is "Quando." Quando is an interrogative that is translated as "when."
Finally, we have "cui." This is an irregular dative form of the relative prounon (Qui, quae, quod - who, which, that). As it is dative, it is translated "To who/which/that.
Right, now we've got all the individual parts, or at least options for them, lets plug them all in.
You say/(To beware/with hole)/what,/when,/ to who.
Now it's just up to me to make my choices. The closest technical translation I get is "You say to beware what, when, to who."
If you toy around for a bit you can make a more idiomatic translation like "You say to beware what, and when to beware, to whomever," but the technical translation as I got it was:
"You say to beware what, when, to who."
Am I close? My Latin teacher would murder me for how I explained what I got, but hopefully I made a little bit of sense. XD