what should start at first when start to develop new module in web App Development?

I am independently working on project using ASP.Net MVC Pattern.let me come into the point,I have no man power. it's ok. but I should consider time manner to deliver product and output. Here,I just want to know whenever come new module i need to analyse and give rough time estimate,it's common stuff i know.My question is what should i start at first thing.I mean,Design Mockup or Backend Stuff,Unit test,Database structure or Stored procedures and so on.which one is best approach to maintain time manner? all techies please give your suggestions?let me know something