Tattooers doing large scale work, often when asked about their process for starting a design, mention planning ahead "as if" the client is getting their whole body tattooed. Ensure that you are taking into consideration not just the area you're going to work on, but also leaving room or shapes for potential additional tattoos or designs to be added on later. Not only does it make it easier for you or the next person, but it makes it easier and more satisfying for the client.
Planning out the design as if it will become a full sleeve is really ideal, and gives you a chance to think of some “What If” scenarios. Things like running up against existing tattoos when the client wants to extend the piece, what other ideas the client might have down the road, or in the case of the clip what would you come up with if they DO decide it’s time for a cover up.
Honestly, it's really common for the client to change their mind or get inspired mid-tattoo. So always keeping that in mind and planning ahead “just in case” can keep you from getting into tight spots. And, could really be incorporated into most of your process and design choices.