These are the search terms you want you advert to show up for. Bear in mind that they have to remain relevant to the subject matter of your landing page. Google has a great tool just for this job in the form of Keyword Planner. It’ll tell you how much competition and potential traffic there is for given keywords, as well as the cost you pay every time someone clicks on it.
These aren't the only marketing strategies that can be executed for next to nothing, so don't limit yourself. Do your research, diversify your strategies, and keep progressing toward your ultimate goals. The beauty of these strategies is that they can work on a passable level with a minimum investment, but if you invest more money, the payoffs start increasing proportionally. You can start off with almost no investment, and by the time you start earning enough revenue to double down on these strategies, you'll be experienced enough to know how to maximize your ROI.
While the previous sentence makes sense to just about everyone reading it, we also know that in practice, content promotion is more often an afterthought than a key part of content planning. It shouldn’t be a special case to improve organic search visibility, social engagement, industry media pickups and influencer shares of your content for all the (relevant) world to see, but the standard when it comes to B2B content marketing.