Some people find a design or simply choose one from the designs already displayed at the shop at the time of arrival. I always recommend people to have an idea of what they actually want and maybe get inspired a little and talk to the artist about it. he or she can help you visualize what you want to can also make some suggestions in order to satisfy you as a customer.
The same way an artist can create a portrait of someone special the artist can apply the same technique to create an animal, a plant, etc. It is better to have a custom made design than bumping into others with the same tattoo. A design can be altered so it don't have to look like someone elses or to avoid making it look too "plain".
A good artist can be very creative and can come up with ideas or a better concept not because he or she wants to charge more, it is because a good artist knows how to provide a satisfactory work. I already talked about people who want to get a tattoo but then complaint about the willingness to pay the artist's worth and some people simply try to find a cheap place and forget all about the important of an artist having a license and hygiene of the shop (later they regret it).
All artists have their own signature design and what I mean by that is that one can look at a tattoo and right away know who did it. Tattoo shops have photo albums of each of their employees which help customers choose who they want once they reviewed each of the artist's work (Some people actually think is to just see how cute the tattoos are or to look at till they're called, LMFAO), unless the customer already have chosen who will encrust the Ink under the top layers of their skin. A small tattoo looks cute in a small area, but some people choose their whole back to get a tattoo the size of a quarter, the same way others want a huge tattoo in a small area (dummy).
Rememebr to always focus on what you want and not to focus on how much it will cost, there is no need to adopt a measure were you feel obligated to spend eight hours getting Inked. You can start a project and give yourself a couple of weeks to either continue or simply finish it, the artist will be waiting for you. Be wise, be original, and be picky.
You can't choose an artist just because someone told you to do so, choose an artist because you like his work and want that artist to work on what you really want, that way you will always be proud of showing what you got. Be patient and don't try bullshitting an artist by having the cojones to compare that artist to another, keep stupid comments to yourself and if you don't get a good vibe then look for someone else, bullshit begins with bullshit so don't attempt to tell a reputable artist how to do the job.
Lei capisce?