Do your research!

A lot of people just walk into a random shop and let the artist do something random.  The problem is, not all tattoo artists are the same.  There are some very good artists out there and there are some terrible ones.  Because this is going to be on you forever most likely, I would suggest researching the places and artists in your area before going out.  Make sure the place you pick is very clean and they take all the necessary precautions to sterilize their instruments.  

Also, make sure that you have seen the artists previous work and that you feel that he or she will do a good job with whatever you decide on. A quick way to test your selected artist is to walk into their shop and tell them what you want.  If you have to provide a small design, do that, but do not give them the full design up front.

Just give them basic information to begin with.  If their are a good artist, they should be able to draw something out of their head that should approximate what you wanted.  If they can't do that, don't go to that shop.  Also, don't be afraid to make adjustments to, or completely reject what they have drawn out.  Don't be afraid to tell them how you really feel!  

You need to trust the artist and be comfortable with their design and talents before moving forward.  This is a permanent marking on you and you want to make sure that everything is right before it goes on you. 

Also...

Don't listen to what people say when they say something like "how are you going to feel about that tattoo when you're 60 years old?".  Because when you're 60 years old, you're going to regret never getting one! You only live once, so do it!

A common mistake people make is leaving the cellophane on WAY too long.  The artist only wraps your arm in cellophane so you can get from the shop to your house without getting it dirty.  I've heard of people that leave it on for hours, which is OKAY, but ideally you should take it off when you get home.  

I've also read horror stories of morons leaving the cellophane on for a week or more!  This is BAD, as your tattoo needs to BREATHE... it is a giant wound on your body!

Also, do not completely saturate the tattoo with A&D ointment.  It will draw the ink out of your skin.  Just put a thin layer of the ointment on, enough to moisturize.  When you over-apply A&D you may have to get the entire tattoo completely redone because the ointment completely faded the ink.

Finally, don't worry about the tattoo having meaning to it.  I think people who say their tattoos have special meaning are not being totally truthful.  If you think something looks nice, get it!  Just think it over for a few weeks/months to make sure it's not something that you think looks nice on paper...then you realize you have it tattooed on you for life.