Make sure that you get the translation correct. This may sound commonplace, but there are scores of Latin tattoos that are improperly translated or are grammatically garbled. It doesn't work to simply run your proposed text through an online translator. For something this important, find a scholar who will translate it correctly for you. Also, know that an exact translation from English to Latin is nearly impossible due to different language origins. Some connotative meaning may be lost, so it is important that your intent is maintained in translation, further necessitating a human translator.
Although not technically in the Latin language, the cross of Christianity is traditionally known as the Latin cross. It is considered a symbol of good luck by many cultures. Religiously, it represents Christianity, the hammer of Thor in Norse mythology, or as representative of the four elements. It can embellished to provide context to your personal meaning for it.
Latin is commonly used in tattoo form to remember those that have passed on. The phrase to use in this instance is "in memoriam," followed by the person's name.
There are a plethora of common Latin phrases that can be used for tattoos. "Ad idem" means "of the same mind." "Fortes et liber" means "strong and free." For those looking toward tomorrow, "mihi cura futuri" means "my concern is the future." For fashionistas, "vestis virum facit" is the traditional version of the phrase "the clothes make the man." Whatever you want, a Latin saying can probably found. An exhaustive collection of Latin phrases is included in the Resources below.
One final word on two common Latin mistakes. The first, the phrase, "nolite te bastardes carborundorum, " which loosely translates as "don't let the bastards grind you down" is incorrect because "carborundorum" is not a Latin word. Lastly, the classic prayer from Samuel L. Jackson's character in "Pulp Fiction" is often translated into Latin incorrectly. Take special care to make sure you stay out of the ignominious company.