Although everyone wants to see immediate results from their SEO campaign, ranking well often takes time. There are many factors that influence the ranking of a website, each of which can affect SEO independently. Google requires time to crawl your website and other off-site content before it can index and rank your pages.
If you make changes to existing pages that are already indexed, those changes can easily influence Google rankings, but they will take time to implement.
If you think fresh content will rank within days, you're mistaken. Ranking a page on Google can take days, weeks, or even months in many cases, depending on how long it takes Google's bots to crawl the page. Keep in mind that there are millions of websites that Google needs to cover, so anticipating instant results when yours pops up is unrealistic.
Furthermore, ranking on page one for a highly competitive keyword is also unrealistic. Give yourself some time to develop more content around certain topics that are more difficult to rank for, and Google will likely reward you within several months' time.
The key here is patience, which truly is a virtue in the world of SEO.