There are three possible ways where you can match your tie or bow tie to your pocket square when it comes to patterns.
1. When the tie or bow tie is a solid color and the pocket square is a neat pattern. In this case, it is rather appealing to have one of the secondary colors in the pattern of the pocket square, to be the main color if the tie or bow tie.
2. When both the tie or bow tie and the pocket square have patterns. Here, it is crucial that the pattern spacing is different. So if your tie or bow tie has thin stripes, have the pocket square be striped in thicker lines or thin stripes with more spacing.
3. When the tie or bow tie is patterned and the pocket square is solid. Here you can also apply the first rule; but have the one of the secondary colors of the pattern on the tie or bow tie to be the main color of the pocket square.