Many tattoos include some form of lettering in them. Sometimes it's a name, date or scripture. People assume because lettering is so common, it must be a rudimentary skill for any tattoo artist. The truth is some artists are better than others in lettering skills. Each artist has their strengths and weaknesses.
If text is a prominent part of your tattoo make sure your artist is talented in this area. Do your research and ask to see previous samples of an artist's lettering and talk to former clients. See live samples of their work if possible. Question the artist and see if they "like" to do lettering.
Once you've decided on a tattoo artist, your next area of research is the lettering. Look into the fonts and lettering styles. There are hundreds of choices and a huge range of resources available - your computer should have a length list of fonts in any “word” program. Once you've narrowed down your font choices, print out your text in that font. Sometimes you'll find individual letters can look quite different in different fonts. You may like the style of one letter but not another and eventually discard that font choice.
Another consideration when it comes to font is the tone of the text. Some fonts are appropriate for say - memorial tattoos whereas playful script may be more appropriate for funny, light-hearted tattoos. You can also ask the artist for his input or suggestions but don't wait until the day of the tattoo to start asking questions. Be prepared and plan ahead.
Probably the most important consideration - spelling, spelling, spelling! There will be no bigger disappointment than getting your tattoo and later realizing you've misspelled a word or name. It happens all the time. This will totally ruin your entire experience. Another factor is color - although black is the most common choice, it isn't your only choice. Just be sure that the color you do choose is easy to read.