My friend Michele Hutchison translates from Dutch to English and has written an excellent piece for English PEN about how experienced translators get better. If you haven't read it yet you should go and do so now, really. If you're a translator, at least.
There's a part two coming so I may be jumping the gun here, but there are two things I want to add from my point of view, having been an inexperienced translator not all that long ago (Michele talks to people with a lot more experience than me, though). The first is that practice makes you better. The mere act of having translated similar phrases or ideas before, having tackled similar challenges and found a passable solution, helps us to try again. This is something I say to people who ask about how to get into translation: practice! But the second thing is that practice alone isn't worth nearly as much as practice with feedback. Sometimes I find myself trying new things out, or indeed repeating old things, that I'm not sure work. Or sometimes I'm just unaware that something I'm doing in my translation only really works in my own mind and not for readers not as submerged in the text as I am. That's where feedback is painful but good. Because slipping into habits is possibly the downside of having experience and practice.
In Berlin and a couple of other cities, we have translation labs where people can get feedback. What I'd really recommend though is a more intensive workshop situation like those offered by the Vice Versa programme in Germany. It's the equivalent of taking a loofa to your translations – it smarts but they look much better afterwards. New Books in German now has a list of this and other opportunities for translators, incidentally.