Firstly, you can get a skull in a wide variety of locations. However, they are usually places on the arm and shoulder area, either as a full or half sleeve, or a smaller skull-style icon.
The simpler designs often incorporate tribal styling as well, which tends to flow around the skull shape - often in the style of pointed wings. If you're looking for something more artistic, then there's a lot of choice. You can find intimidating hellish designs which usually include lots of bold, striking color to illustrate flames, fire, and other ghoulish design ideas.
For a more comic effect, you can find designs which include skulls smoking cigarettes, or cartoonish design. For a more chilling effect, you can go for a demonic design, which often includes horror elements such as blood, grim reaper scythes, and swords or other weapons.
Some of the artistic designs occasionally use an "almost human" style of face, with parts of the skull creeping through. This can create a chilling, haunting effect. But be warned - your tattoo is sure to scare kids!
Death and demonic themes are hugely prevalent in skull designs, so most of the designs are created to give an intimidating feel. However, some of them also include flowers - particularly roses - for a bitter-sweet romantic feel.
If you're looking for something unconventional, a little scary, or funny - then getting a skull tattoo may be for you. But remember, there's many, many different designs in this category - so it's worth doing some research before you pick one in particular.