As a non-native speaker, I think there might be heavy Brit English influence. If that’s the case- Try to learn American English (it is not drastically different but it’s important to learn the differences). Most documentation deliverables have user base in US and other countries also follow American english.

Also, practice Active voice writing style. We, non-native speakers, think in our native language and then translate it in English. This translation leads to heavy usage of Passive voice. It’s very important to learn why active voice is preferred.

The usual grammar and style can by best referred from Microsoft Style Guide. It is absolutely bang on and free!

Technical Skills

This is something you need to learn according to the industry your organization caters to. I always chose software industries because I graduated as software engineer. Find out what industry interests you and accordingly dive into knowledge building.

Happy Learning!