I've written poetry since high school, but only recently gotten "serious" about it. I write every day (when it isn't finals season) on a wordpress blog, and I read a lot of poetry, pretty much by whoever I can find; recently this has been Keaton Henson, Warsan Shire, Aida Mitsuo, Michelle Smith, Tanaka Eris, John Keats, Robert Service, and lots of tanka and haiku by various authors. I think it's hard not to at least partially imitate someone you've read, even unconsciously.
I've also been reading the book "next word, better word" which has helped me a lot in terms of learning the formal elements of poetry and how they effect the more intangible aspects.
edit: spelling
Different poets use different approaches.
I heard that Yeats wrote his thoughts in prose and then sculpted that into poetry.
I think Roethke kept a notebook where he jotted down interesting lines and then tried to connect them to each other.
This book helped me a lot when I was going through a dry spell.