I once taught someone from Spain who worked for a drug, or pharmaceutical, company. He had a hard time comprehending native speaker speech. His comprehension in the conference rooms improved after I introduced him to the informal and relaxed speech sounds of American English. So much for "formal speaking" in business. It's simply not there as much as some people would like to insist that it is.
Here's another idea. Write what you hear even if you can't hear all of it. Then go back and try to fill in the blanks. Oftentimes it's more difficult to hear the structure words and contractions. So for example, you might hear "I __ told you", when the speaker really said "I've told you". Or you might hear "I __ tell you", when the speaker really said "I'd tell you". I used this method once, and it seemed to be helpful. When you go back to fill in the blanks, you might find in some cases you can figure out what the speaker said because now listening becomes a grammar exercise.
I recommend the old American TV show M*A*S*H to practice listening to more relaxed and informal pronunciation. Watch Star Trek for speech that sounds clearer and more well-formed. The speech in Star Trek is spoken in a kind of scientific register, which is why it might sound clearer - I said "might".
Also, try to be in the habit of using contractions for all of your spoken language. We usually use contractions when we speak. If we need to emphasize or add clarity for some reason, there's less chance that we'll use contractions. I would always use contractions. I think this will help you hear contractions better.
There are a number of ways to answer your question, and I might be able to think of things that I haven't even tried yet, as I only do what works best in each situation. If I think of anything else that I feel might be useful, I'll post it.
Student or Learner