Just like the quote here about looking at a million paintings, reading poetry will heighten a writers level of taste and work. The answer to improving really is by reading and exposing ourselves to great work. This morning I was reading poetry in the journal Agni. They've really got a handle on great poetry. I'm moved by every piece. I don't know why aspiring poets aren't reading this stuff like crazy. And I don't really see how people are going to improve much without doing so. Sure, there can be exceptions, maybe? But I have a feeling most poets that are publishing read a good amount. And even if you're not looking to publish, you're looking to improve. Reading poetry is going to make you better. This is something that just happens. I assume most people writing poetry like poetry. My advice is to read good poetry every day for a year. I would be surprised if that didn't improve the level of writing and also help when it comes to critiquing the work of others.
