hi cosmo-torun,
With a search engine, anyone can easily find some good "how to write good scientific English" guides, but here are a few that seem especially useful. For our writing of journal articles, PhD theses, and lic/mag theses, I think that these could be very useful. Even if you write in Polish, many of the principles are likely to be the same.
* Grammatical and scientific correctness are necessary, but not sufficient, to provide a high probability of the reader understanding some scientific text. Gopen and Swan argue that writing short sentences is not necessarily enough either; and avoiding technical language does not necessarily improve readability either. They provide concrete examples and show how and why the examples could be rewritten more clearly:
http://www.americanscientist.org/issues/pub/the-science-of-scientific-writin...
* The "see also" section of this Wikipedia article seems to be its most useful part: https://en.wikipedia.org/wiki/Scientific_writing#See_also https://en.wikipedia.org/w/index.php?title=Scientific_writing&oldid=6275...
* European scientific writing guidelines, including a partly Polish guideline of how to write in English: http://www.ease.org.uk/publications/author-guidelines http://www.ease.org.uk/sites/default/files/ease_guidelines-june2014-polish.p...
Cheers Boud