At first the thing to consider is the overall look and feel that you want your kitchen to have, whether that be warm or cool tones, rustic or contemporary finishes.
One way to make these decisions is by having a range of designs that you would like to implement into your kitchen (Pinterest is one way to store these ideas). This a great way to get an idea of your personal style, and what you like in a kitchen, thus steering you and your designer towards choices that will build up your design. Minimalism, Attention to detail, Originality and Timelessness are things to consider from a design aspect of a kitchen.
Colour is an important aspect of any kitchen, and should be decided on with a few different factors in mind, such as the kitchen furniture, the countertop, and the kitchen flooring, either working in contrast with them or in sync with the active colour scheme. There are two ways to go when considering its impact on the flooring. Keeping the floor and splashback identical to create a continuous flow of colour and shape, or changing an element such as format and going with a similar finish, vice versa.
A common technical design over-site on many kitchen backsplashes is the covering height. Dependent upon your kitchens design, open plan or not, the height of you covering can change the aesthetic of your kitchen entirely. The options vary from low band to full height covering and anything in between.
No matter what you choose the design of your kitchen will be pulled together by its detail and elements, so it all comes down to the result you want to achieve and from the finishes that you choose.