Pretty much nailed it.
You want to read as much as possible (especially so if English is your second language), but the best thing to do is just write and write and write.
But the important part is to then leave it a bit. An hour, a day, a week, however long, and then go back to look at it again and analyse it. Pick it apart a little bit and reword the bits that jump out at you.
As for simple tips there's one thing I always end up having to change up in books.>Try not to repeat the same word too much in too-short a space.
This is especially bad in some fantasy and sci-fi novels I've edited, where there just arent many ways to say some particular thing. Its really noticable if a character is a mage and you end up getting a paragraph like"Anon flung her hand out towards the thief, her fingers making a complex magical sigil as she summoned the magic to her. She felt a tingling spread from her fingertips, down her arm, across her chest and to her heart where all magic resides - and then it flashed outwards, a blue electric whiplash sending the man flying into the wall."
Stuff like magical / magic / magic showing up three times in this short bit will end up really standing out to people. It can happen with just about anything, this is just based on a recent example I bumped into a bunch.
One book had a fight between two mages which ended up only spreading across maybe two pages, but used the word magic about 3.4 zillion times.
I guess the other big thing to suggest is 'When writing dialogue, read it out aloud to yourself'.
A lot of people end up writing dialogue where people never use normal speech patterns - like never using contractions like can't
or 'couldn't* and the like. It makes their characters all sound always formal, which isnt usually what you want at all.
Reading it aloud isn't always going to work, b ut in a lot of cases it'll help you iron out weird wrinkles in conversations!