That's a very vague question for SEO. SEO is huge, and pretty complex. Here's a few:
- On-Site SEO
Make sure your on-site SEO is properly optimized. This is crucial to ranking & will save you a lot of money. Make sure not to over-optimize as that will hurt your website.
- Content on Your Website
Your website must have RICH content, and preferably lots of it. Start a blog, do proper internal linking (many guides online on how to do it) & give value.
- Internal Linking
Start a blog on the site. Write quality useful articles that your readers will enjoy & benefit from. Also write a few blog posts directly related to your main keywords and link to them via your anchors to build relevancy. There's guides online on internal linking, I'd suggest you start reading.
- SSL Certificate (https)
Simply helps (minor).
- Diversify Your Link Building
I'm not only talking about proper keyword diversity but also web-platform. Build many types of high quality links. Use well researched & written content to build your links.
Build links to your main money keywords, LSI/Long-tails, the URL itself, branded, generics (click here, more, get more information) and etc.
- PBNs
Before doing these or you can do the simultaneously, build a proper SEO foundation for your website (above). Use a trusted network of HQ PBNs if you're going to be using them. Don't try to look for "cheap" offers. You get what you pay for.
- Guest Posts
Neil Patel will help you with this one:
https://www.quicksprout.com/the-advanced-guide-to-link-building-chapter-10/
This is just the tip of the ice-berg. I highly suggest you spend quite some time reading on SEO as there are a lot of factors that play in.
Luka