TIP #2: If you don't pay to promote an advert, very few people will see it
Organic reach is much smaller than it once was (you may have noticed your posts don't get as much likes / comments or shares anymore). With really engaging content you can still achieve a good organic reach but it is so much easier and more effective to reach a lot of people when you pay to promote a post. You don't have to spend a lot of money either - start off with a budget of just £3.50 to promote a post and see how it goes. If something performs well, then spend more money.
HINT: If something has a good organic reach it will do even better if promoted - test it for yourself.