Paid backlinks are bad. Unless you are highly experienced you will get your website penalised when Google sees what you are doing. Manual link building is the way to go for in-house SEO. This will give you long term high rankings in Google, assuming your on-page SEO is up to scratch.

Use a company email address. Approaching any sites ranking for keywords you are interested in, plus the general niche. Sometimes it will make more sense to link to an inner page offering useful information. 

Quality Content is essential for manual link building

Cheaply written blog posts aren't good enough, you need quality information to attract natural links and offer up when manual link building.

For manual links you need to have genuinely helpful informational pages that will add value to an article on someone's website.  

Use Google For Content Ideas

For ideas look at questions in Google when typing in keywords on the rank checker list - Google shows "People Also Ask" questions. Answer these and similar questions. These pages will also bring in good traffic. 

Get manual links on new websites

HARO can be used to get press links for any related topics and this works by someone from the company giving a quote. You sign up to the nearest niche e.g. technology, then everyday you get a list of articles that journalists need to write about. 

When one is similar to your content or market, you contact them and offer a quote. The quote could be a statistic like According to John Jones, the CEO of My Business, "50% of businesses use AI in logistics currently and 75% will use it by the end of 2024". 

Wikipedia is your friend

Wikipedia would be a good place to get a link. Anyone can edit Wikipedia. If you don't have an informational page, create one with useful data. Then add it to the references on the most relevant Wikipedia page. You may even be able to add text to the page and weave your link into the text.