Are you running a business now? Do you have plans in the near future to start that business, farm, organization, charity, write a book or launch a music video? Whatever it is, you need to build a community around it now. Why? Because online marketing will become very expensive.
Actually it has already started to be costly. The same way TV advertising is out of reach to many, online advertising is headed that route.
You need to start building a community around that niche you want to fill well before you open doors. This community will be your evangelists who will spread the word thereby reducing initial marketing costs tremendously.
Facebook is the best place to build your community. It has amazing targeting options allowing you to reach that person you need to instantly. The only flaw with Facebook is you will only reach a few of your fans organically (without pay). To address this, you only have to ask your fans to follow you on organic oriented platforms such as Instagram where you will reach all your followers.
A strong community will shield you from the frequent changes by these platforms that will make it harder and expensive to market.