You can't possibly serve all the people in the world so just concentrate on serving a few people in your chosen niche. Serve them well and you will have a customer for life.
Your customers become your friend and spread the word to other like minded people. This is because you are doing one basic thing for a particular group of people and they understand what it is you are offering.
This also makes your marketing easier. Focusing your efforts on your niche gives people a clear message what you are about. Word of mouth is the best advertising you can get - and it's totally free - so give the very best service to a small group of people and you won't look back.

