أنشئ حسابًا أو سجّل الدخول للانضمام إلى مجتمعك المهني.
Well, that would be match to the identity of the client's business and you can play any kind that theme but still a theme that will recognize the company that would be their ads.
There is no process per se, it depends on the client's brief, their corporate identity, and what they want to achieve, so each time it is a different way of proceeding.
as the colleagues below said, there is no rules for how make it, but in first get all requirments >>> get ideas through searching over the internet and find yours, draw your sketch on the papers, start using photoshop or any software you use, slice it, test it & you done.
Its based on client input some time they give details instruction with refeence sites what they want and some time client give nothing from there side and you have to do hit and try job , give 2-3 mockups normally client accept1 from them