Knowing what you want, as in the design of the tattoo itself, is only one step. You also need to know where you want the tattoo.
Long-term, the place you get the tattoo put matters because you may want to get it a place that you can cover up with clothing, or even a place that you can add to (per Alt Press). For example, if you're getting tattoos on your arm and you later want to build it into a sleeve, placement and pieces matter so the sleeve can be a cohesive piece later down the road. Many people end up getting tattoos removed when they don't fit with their process later, or if they're working in a career where they don't want to be tattooed visibly.
Another thing to consider is where you go for your tattoo. Not all tattoo artists are the same, and many specialize in specific styles. Some are better with traditional tattoos, while others are better with more modern ones. Some do great color work, others specialize in black and white looks. If you want a specific kind of tattoo or style, or even if you want font and words, do your research before booking. You also want to make sure you are going to a studio that is clean and well-reviewed (per Bustle).