Please take into consideration the following factors when creating your embossed design.
The finest detail possible for an emboss is 1pt.
Some stocks such as more dense or coated stocks have lower tolerances for embossing, so details will need to be larger. Other factors, including blind embossing vs registered embossing will affect how fine the detail should be in your emboss design.
See: Finest Detail for an Emboss.
The safety margin for embossed artwork should be kept at least 0.125 inches away from the trim lines on all sides for most orders. A 2-ply embossed order will require a larger safety margin of at least 0.25 inches away from the trim lines on all sides. It is also possible for the artwork to bleed to the edge, in which case 0.125 inches of bleed will be required.
A reverse impression of the embossed artwork (known as a deboss) will show through to the other side of the card. You can use a 2-ply option where two cards are mounted together to hide the deboss on the back (leaving the back side flat) although this is only recommended with coated stocks. Some designers have found innovative uses for the deboss on the back of the card, incorporating both effects into their artwork. This is an effective design consideration that can create a very memorable card, however please keep in mind that if your embossed artwork includes embossed text, it will only be forward reading on the embossed side.