If you follow this guide, you will have no problems wearing your men's gilet correctly:
The men's gilet should generally be long enough to cover the waistband of the trousers. However, it should not go below the hips.
As a rule, the lowest button of the suit gilet is worn open.
The back tab is adjusted so that the gilet fits comfortably. It should neither be too tight and stretchy nor stand too far away from the body.
If the men's gilet has a lapel, make sure that it lies flat against the gilet and does not stand up.
If you have a pocket watch with you, the watch is kept in one of the belly pockets and the watch chain is attached to a centre button slot.
Should you be carrying a pocket square, fold it so that a nice lace peeks out half or a third of the way from the breast pocket of your men's gilet.