Define the purpose of your app - Most apps are created to solve a problem or to improve certain aspects of life. What are the core functions of your app? How is it going to help the use? The entire process of your app creation will be faster if you have a definite purpose in mind.
Do some research - Make sure that your app is unique. Research whether there's already something already out there that works like your app. Research the technical requirements for your app too. This will help you understand whether it is technically possible to turn your idea into reality..
Work on your app's wireframes and storyboard - Wireframing is the process of creating an app prototype. There are a number of online tools that you can use for this task. Create a storyboard once your wireframes are completed. A storyboard will show the connection between each screen and how users can navigate though your app.
Build your app's backend - Make a sketch of your servers, APIs and data diagrams based on your wireframes and storyboards. Where technical limitations become apparent, modify your wireframes and storyboards. You will need the help of a developer in setting-up APIs, databases, servers and storage solutions. If you're looking for skilled developers, you can visit them here.
Do a test run for your proptype- It's not enough to review your app on your own. Ask other people to try your app and provide an honest evaluation of its capabilities. Take note of any broken links that affect quality user experience.
Design your app's individual screens - Decide on the color and design of your app's wireframes. Let your designer come up with a high-resolution version of these.
Test your app again and make any necessary revisions - Test your app after the actual design has been implemented. Ask other people to try it again and to provide feedback once they have used it. You can ask your developer to improve the backend or your designer to change the layout based on the suggestions you gather from your testers.
Besides having a brilliant idea, you will also need a big enough budget to create your unique app. Do you want to know how to raise the funds you are going to need? Read this neat infographic from Buzinga.