The sheer facts point to continued explosive growth of online ads. And we're still in the infancy of the internet. The earlier you capitalize on this industry, the quicker you can build it into a formidable online business. Study and learn all the intricacies of advertising on platforms like Facebook and Google. Find courses, or use the free material available from a multitude of platforms to become a seasoned pro. 
The internet changes so fast that one year online equals about five years in the real world. But the principles of how to start and grow a successful online business haven't changed at all. If you're just starting a small business online, stick to this sequence. If you've been online awhile, do a quick review and see if there's a step you're neglecting, or never got around to doing in the first place. You can't go wrong with the basics.