Once you've found the right keywords & some main papers, try to find reviews.

• Literature reviews qualitatively review all the papers on a topic.
• Meta-analyses try to collect effects from multiple papers on the topic to give a quantitative answer.
• Textbooks are used to present the field the way experts want a beginner to learn about it.

It can be helpful to type a keyword with the words "review" or "meta-analysis" in Google Scholar. 

These are some of the essential things you should know:

• Sci-Hub is helpful to get access to papers. Alternatively, emailing authors can give you access to papers, but it tends to slow reading down.
• Google Books can help you find specifics in a particular book.
• Don't be hesitant to take courses first. It will provide a background on the topic.

Experts are very willing to talk to you.

Once you gained some understanding in a field, follow citation trails. 

There will often be dozens of other papers cited and can result in an extensive reading list. Thus it is helpful to limit yourself to the few most promising ones.

Citations should have 2 major factors: 

1. Frequency 
2. Relevance. 

Always remember that works cited more often are more centralized to a topic.

There is always something more to read which can potentially give you more insights on your topic. 

You will never reach a point that will tell you you're done.

Since, research is open-ended, it can be hard to keep up.

Thus, it is better to decide before starting that how much time you want to commit to research.