The Triangle fold is probably the most common of the handkerchief folds. It can work well for both casual and formal occasions.
Suggested handkerchief for this folding style:
White Mens Handkerchief With Satin Stripes
Fold the hankerchief in half.
Fold the handkerchief into quarters.
Orient the hankerchief up into a diamond shape, fold the left hand side over one thirds and then repeat on the right hand side.
Fold the bottom half over to meet the top edge of the handkerchief and tuck the handkerchief into your suit's breast pocket.