For me personally... I had an idea and found just the right person to do it through references. Obviously a full sleeve is not something to go into without much thought. I have one other tat, and enjoyed the experience.
So, I have always been interested in asian cultures, I am a pisces and I also study Bonsai... I left the rest to the artist. He is very good. He has studied IREZUMI (traditional Japanese tattooing) and actually prefers that style and would be happy doing said style almost exclusively. A lot of artists don't like to be told what to do so I was lucky in finding somebody with great skill that could take my list of about 20 words and run with it.
Here'e the cool thing... the first 2 sessions were discussed beforehand... a few koi. We talked about the grand idea of koi ascending up out of the waters into a dragonfish on my shoulder and maybe over into some of the chest. I was cool with that idea. Well I show up at the 3rd session and he had dropped the dragonfish and added a tree... I was blown away because this is really what I always wanted. Through our first 2 sessions we got to know each other pretty good, he is my age and went to a rival HS, and during our conversations he was astute enough to actually LISTEN to what I was saying. Imagine that. So I am more than pleased!
Here are a few suggestions if you decide to do something like this:
1. What do you do for a living? Will the tattoo have any adverse affects on your livelyhood? What about your family?
2. What can you afford? Do you have to save up a bit before jumping in?
3. Have you did research on what you want done? Do it mean anything to you, or could it possibly be regretted 10 years down the line?
4. Have you asked for references for an artist? Make sure to do your homework... you are gonna' pay good money for this, and it's on you till death so make absolutely sure YOU get what YOU wanted.
Hope this helps a bit...