What is your favorite technique for improving your writing?
Strengthening verbs works well for me. Copying another writer line-by-line doesn’t work as well, although I do learn a lot by trying to edit a passage from a writer I consider better. (I delete these edits afterword, I don’t have any illusions that they are “my” work).
Now I’m looking for other techniques to try. Does anyone have suggestions?
First, welcome to the community! 
I don’t know if I use any techniques as such. (I might need to start!) Consciously using stronger verbs has been so important for me. Similarly, taking time to find single words that can replace two others has helped lots (very fast > rapid; large and hollow > cavernous).
One thing Brandon Sanderson said really stuck in my mind: Consider how you’ll write your scene so that it could be someone’s favourite. After I heard that, I became determined to recite that to myself at all times, insisting that I never write a purely meh scene. Even if it’s just mundane dialogue, something about it needs to be worthy of someone’s love. Whether I can live up to this goal is another matter, but I’ll try.
I don’t know if that’s what you meant, but it’s helped me a lot.
I am still writing my first rough draft of a novel. Haven’t quite gotten to refining the wording yet, but one thing I do constantly is kick my verbs out of passive tense. I naturally write in a passive voice and I hate it!
I use the ‘find’ facility for the word ‘that’. My worst habit is to have 'that’s scattered throughout. I scrutinise each one to determine if the sentence can survive without it, if yes, out it goes. Another is ‘it’s’. Again, I ask each time if I can substitute ‘it is’ - if I can, then it stays. If not, out the apostrophe goes. My first agent said my writing was ‘clean’. I think these two little things helped earn that comment.
I like to look for and create different rhythms. For example, if I have a scene where all the (prose, not dialogue) sentences are the same length, they tend to feel like a laundry list. I tend to write lean, and fleshing out a sentence is a challenge. This is where sensory immersion helps.
For inspiration, I’ll read anything by the playwright Christopher Fry. As old fashioned and outdated his plays might be for modern readers, his purposeful use of language is like a symphony to this reader. 
I have the opposite issue, Lita. I tend toward long, complex sentences and I have been making a concerted effort to go back and break them up into multiple sentences of their own.
I edit fanfiction for another fanfic writer who’s first language is Danish. She has amazing English, but there are things she gets swapped around, and sentence structure ends up backwards sometimes, so I like to completely line edit at least 1-2 pages of her work per day. That way, I can viciously rip something apart without feeling attached to it.
Two of my favorite things, in no particular order: quatrains and verse.