SEO is an art, and one which continues to change consistently over time, there are many different ways which you can use to improve your SEO and get to the top of the search positions, but there are trends and techniques which get used over and over again in order to get to the top. These change over time, Google is always moving and evolving and trying to improve its product, which is effectively search results for its users.
When SEO first started, things were a little simpler. The number of links you have pointing to your website is still a very important factor, but back in the day it was probably the most important, and it mattered less where those links came from, and just chucking a lot of links at a site, wherever they were from, could do wonders for a website.
SEO has moved to a more social algorithm which accounts for factors such as your social following and shares of your content. Though this is a great method of finding good results, links are still vital, and create a great basis of your SEO strategy, however the focus is now on quality rather than quantity, a link from Nasa for instance holds a lot more weight than from a spammy site, and the closer associated your site is to those which are highly regarded, the better.
Sites like the best seo company singapore can help to implement good quality strategies for sites of all different niches and sizes.