1-Do not tattoo someones name or portrait
 It may feel like the person will always be in your heart and deserves to  get that special attention. Unfortunately, this is one of the biggest  and most common mistakes. The reason is...no matter how you feel, how in  love you are right now, you may not last forever. You do not want an  ex's name on you forever, especially when you find someone new. But  there is an exception : this may be a good idea if you are considering  the name or face of your child or parents.
 See also : Gwyneth Paltrow expresses love for Chris  Martin with a ‘C’ tattoo! 
 2- Do not get a cheap and nasty tattoo
As Kat Von D from the hit TV show LA Ink says:
"Good tattoos aren't cheap and cheap tattoos aren't good. Far too many  times, people choose an artist based on price. That should be the last  priority on your list when it comes to getting a tattoo." (Source
 3- Never agree to get a tattoo when you're in the wrong state of mind
If you're drunk, depressed or under pressure, don't get a tattoo done.  You know it's a whim when you find yourself in a tattoo studio and you  hadn't even considered getting a tattoo the night before! It's good to  be spontaneous, but not with something that will last you the rest of  your life. Source
 4- Choose the right design
 Choosing the right design is absolutely vital to the amount of pleasure  you get from your tattoo. Do not compromise on what you want. The final  choice of tattoo design must be yours. After all, you're the one who'll  have to live with it. Source
 5- Finally, the tattoo and aftercare
 On the day your tattoo is created, a better overall affect will be  achieved if you are well slept and well fed. If you are tense, full of  stress or restless, it will take longer and the tattoo won't be as  perfect. Once completed, most tattoos will take up to a month to heal  properly. During the whole healing process, follow the aftercare  recommendations of your tattoo artist. Source