I used to get right down at DS1's level and quietly say, "come and have a chat to Mummy" when his emotions were escalating, or when he seemed to be too overwhelmed to get his message across. I would take him a few steps away and sit him on my lap for a close quiet talk together.
I found that this helped distract DS1 from whatever had become an issue and gave him some space from the source of the problem. I would give him a big hug (even when he wasn't keen on it!) and tell him "I love you, even when you're cranky/upset with me/frustrated": in the process he got some physical reassurance and comfort while we quietly talked about what had happened or what was causing a problem.
Words didn't start flowing for DS1 until somewhere between 2-2.5 yrs, so between the ages of about 1-2 yrs I would try to be really patient and ask lots of simple questions that I knew DS1 could answer in really simple language or by gesturing (yes/no, point to what's making you sad/cranky, point to what would make you happy/ what you need etc).
I found it useful to try to demonstrate a feeling in a humorous way and then start fishing for what DS1 was feeling... such as [scrunching fists, grimacing, and making a silly "Arrrghhh!" noise] asking, "are you feeling frustrated?". The sillier the better to break the tension.
Now that DS1 has lots of words, containing the excitement of the story he is trying to tell can be more the issue - a happy one at that though. I now find myself saying "stop/slow down"....[big pause]...."now try again just a little slower", and when he does get his message across I say "Oh silly Mummy... of course that was what you trying to tell me...my ears couldn't keep up!" or something equally as silly but with some positive reinforcement.
Oh, such a beautiful stage!!