What are the first steps in starting a good business?

I'm gonna assume you're talking about a B2C idea. You should validate before even thinking about registering your company. A common mistake is building before you ask whether a person would pay to use it.
Bear in mind there's a big difference between someone willing to use it and someone willing to pay for it. It's important to know who your first five customers are and whether you can reach them.
As for fear of the idea of getting stolen - don't worry. Ideas are cheap, execution matters more.

I think like many others who have shared here, validating the idea with an MVP should be the core of the business. To give some further insight/examples, here's a diagram of 'how' to do it:

But before the MVP and plunging any limited resources into building and enhancing it, conducting user interviews to determine what features an MVP will have is important too. User interviews usually come in two stages: empathizing, and then ideating.

1) Emp: the trick is to not tell the potential user what you want to build. Ask questions about his/her life in general, and fish out pain points faced in going about their everyday life.

2) only when those PPs are uncovered (at least in your notes), then ask, you mentioned you have trouble with xxx, how would it be like if I can solve it? What would be a good way to do it for you? How much would you pay?

And Singapore being a practical society, MVP and user interviews can all be done in your spare time, as a side hustle, means you don't have to quit your day jobs! (provided you are willing to put in an additional 30 hours a week to do this, cos being in a startup means 74-hour weeks are commonplace anyway)

A few tools to help you in this process are pitchspot.co and thestartupbuddy.co