Good afternoon �

I Am a student am trying to build a mobile app for some targeted group of businesses. 
And I'm seeking for assistance and advice on what to do and what to avoid in terms of building an mobile application. The time and cost implications.

Thank you

This question is tricky to answer, but cause there's no specific detail you've provided for what you want to do...

Maybe you can rephrase your question to cover some more ground on exactly what you want