The best way to improve your google ranking is providing good content.
Content is king. Best is to get new content up on a regular basis. When your website gets content updates, the search engine spiders will look again to you site in time.
Loading speed comes second after this. The internet is very fast, and no one wants to wait until something shows up. A visitor decides often within seconds it he wants to remain on a website or not. If there is nothing to be seen within these seconds, he will be gone to the next website.
When you write your content you can use certain keywords on your pages. These are words that you want the search eninges to associate with your page, so when someone searches after these keywords your website eventually shows up in the first results.
So you use them often, in headings, page titles and as alt-Text for pictures. But you should not overdo it, don't spam your site with keywords, instead use them in a meaningful way within your content.
There is more, but this can give a start.