Learn Italian: Ci vuole una buona tecnica per cadere sul tatami. - You need good technique to fall on the tatami.

Ci vuole comes from the verb volerci and means "it takes" or "is required." It is used for objective, general necessity—meaning anyone falling on a tatami needs this technique. In contrast, avere bisogno di expresses a specific, personal need (like saying "I personally need a technique").

What decides the conjugation of ci vuole in this sentence?

The verb agrees with the thing that is needed, which acts as the subject. Here, the subject is una buona tecnica. Because it is singular, the verb is in the third-person singular (vuole). If you needed something plural, like "good reflexes," it would change to ci vogliono buoni riflessi.

Could I put the adjective after the noun and say una tecnica buona?

You could, but una buona tecnica sounds much more natural here. Placing common adjectives like buono before the noun is typical in Italian when describing an inherent, expected, or abstract quality. Placing it after the noun emphasizes it restrictively to contrast it with a bad technique, which isn't the point of this general statement.

Why do we use the preposition per before cadere?