I've been planning to get full sleeves done for a few years now, but I'm still refining the design concept, and searching for the right artist. I have 6 tattoos already, and I'd have to say - above all: take your time.
This is an expression of who you are, and there's no such thing as too much preparation before you commit to a design or an artist. Find someone whose style and demeanor "fit" with you, and you will be happy with the results.
There's nothing worse than "what if" - what if I had taken more time to be sure the design was what I wanted, what if I had taken more time to find the right artist for me... On the flip-side of that - there's nothing more satisfying than having a piece you are 100% satisfied with, and that you can be proud of and cherish for the rest of your life.