said 3 months, 4 weeks ago:
That’s a broad question and there are many ways you can take to trace your path and reach your goal. First of all you definitely need to know where is your audience hanging out (as @rich-brooks) correctly stated, what are their interests, what do you have to offer, if you have a budget to build your list or not, if you can create good content or not, etc, etc.
Building a list could take months or some few days, depending on several factors.
Hope to hear more about your business soon.