I have decided to post this because I believe to many of us are missing this essential element of a suit and because their are a few things you should know before you go jumping into adding a pocket square to your arsenal of fashion treasures! First, how to fold them! That is addressed here and is a great guide on how-to fold for different events. One thing to keep in mind is that the pre-folded packet squares look pre-folded and in turn look pretty bad! Avoid them at all costs!
Second, is matching / coloring. This is so important. Many companies today sell matching ties, pocket squares, and cufflings. This is a horrible fashion no-no! A white pocket square is always safe. It is conservative, clean, and classy and you can't ever go wrong! If you choose to go with a colored pocket square, it should match in the sense that it coordinates.
For Example:
A red tie with a blue accent color could be matched with a pocket square that compliments the blue in the tie. It should have a different pattern and not look like it was made to match the tie. Here is an example in photo. You can see how the red pocket square is a great compliment to the tie. Patterns are similar but not the same. Remember if you want to be safe, white is always a great choice. You can't ever go wrong!