When it comes to doing planetary squares, the sign of the moon doesn't matter as much since you are working directly with the energy of the planet. Just make sure the moon isn't void when you first start the square.
That being said you can get a minor boost to your working if the moon is in a good sign. For example if you did a love working with a Venus Square during a waxing Taurus moon, it would be slightly stronger. But a Venus Square for love during a Pisces moon, even if waning would still work just fine.