Just get into SEO – what's your only advice?

Try your best to follow and understand Google's Webmaster Guidelines.

But the most important thing you should not do is to change the URLs of your website over the years (if you really want stable SEO traffic to come to your website over many years, you should not change the URLs). Avoid using a CMS that automatically generates many URLs for the same page. WordPress as a CMS is probably better than most other CMS because it is easy to control the URLs of your website. If you prefer to build your website without CMS, you should follow the "Never change URLs" rule.