Any large tattoo should flow with the shape of the body it adorns. Placement is also very important and will affect the overall impact of the tattoo. It is important to decide on the overall theme before finding a style of artwork that appeals to you, or you may be influenced by attractive art into designing a piece that does not really suit your needs.
Remember that most tattoo artists have a specialty or a preferred style of tattooing. Schedule consultations with prospective artists and show them examples of the style of tattoo you are looking for. Always ask to see their portfolios or social media pages in order to view their work. Once you have chosen a reputable artist who works in a style you like, he or she should likely trace a life size outline of the area you wish to cover. This creates a canvas for you both to work on during the design phase.
It's important to choose an artist who has a compatible creative vision. The artist may suggest changes to the layout of the tattoo, but he or she should make every effort to incorporate all of the design elements you specify. Allow your artist creative freedom where possible in the design of the piece to make use of their professional expertise, but provide as much guidance as possible to ensure that you are happy with the final, permanent result.