Filtering newbie

[Losko]

Hi, I use to encode my movies using x265 for space saving and I've read sometimes pre-filtering may raise content compressibility, now I can play with avisynth but I'm a total newbie at filtering.
First of all:

1. does more compressibility mean the same content may be encoded faster?
2. does more compressibility mean the same content may be encoded in a smaller size?

And then:

1. where will I find some readings for a beginner?
2. any suggestion for not going through trial and error?

Thank you for any hints.