This is from my personal experience farming Blueberry points,
if you can, do Group Quests as much as possible, once your complete 10 different takes in a group, one "difficult" (They're not really) task will pop up, that'll either want you take a photos with you and your friends wearing certain things or require making a certain picnic sandwich or even a variety of random things and these will often reward you with 300, 500, or sometimes even 1000 BP!
Source for Group Questing---https://www.youtube.com/watch?v=aVgkjnPaV2I
However if you don't have a way to play Union Circle, the best way would be to do as many small easy tasks as possible, don't get stuck trying to catch a Pokemon in the Savannah Biome, if you have two quests that require things that could easily be completed in your current Biome the main things that takes the longest is trying to find certain types to catch you will still get bigger tasks like you do in Union Circle, they'll just have much smaller BP outputs.
Source for Solo Questing---https://www.youtube.com/watch?v=a7na0O8DvF0
this video also explains the differences between the two probably better than I did.
https://www.youtube.com/watch?v=dfg0gPlm30M
