The next step is to check out the SAP Fiori design guidelines which can be found on the SAP website using the following link http://experience.sap.com/fiori-guidelines/. These guidelines will help you understand what the Fiori design philosophy means and how you can create your own apps based on it. This includes everything including the design Principles, UI Overview, Grid Layout, Navigation, Animation, Typography, Colours, Icons, Theming etc. There is also a Prototyping Kit which allows you to design your app within a PDF document before you do any coding.
There is also an online theme designer provided by SAP which allows you to actually design your own themes which can be download and presumably used in your own system. You will need to register for this but it is free for anyone to do!