Hello hello Ego~
Welcome to Iwaku!! I hope you find lots of RPs that tickle your fancy, and even make tons of friends through those RPs! (I know I have and it's one of the best feelings ever~)
Personally, I've found a way to improve my writing by just writing! Like Firejay said, writing with other excellent writers just makes your writing so much better! (Picking up on the idiosyncrasies and intricacies of a person's writing is my thing as well~)
As everyone has said before as well, the Refining Writing section is very useful~ Even if you don't end up writing anything in the section, there's always something to learn there by reading other people's work!
Anyway, I hope you have a wonderful time on the site and I hope I see you around~