This Seeking Tech guide will explain how you can get free PlayStation Star points without being subscribed to PlayStation Plus or purchasing anything from the PlayStation Store.
Use the following video as a visual aide:
For the first step, make sure you start the campaign for PlayStation Tournaments. These will occasionally pop up from time to time, even if you already completed the same one previously.
Next, you need to download Naraka Bladepoint from the PlayStation Store. Since it is a free-to-play online title, you do not need to subscribe to PS Plus.
After downloading it, navigate over to the Naraka icon on the home screen, and then press down until you see the Upcoming Tournaments section.
You should then register for a tournament.
Once you are registered, you need to wait until the tournament ends. You do not have to boot up Naraka or play in the actual tournament to qualify.
When the campaign is completed, the points should appear in your account.