I think sometimes it is really important to remember that actions speak louder then words and sometimes in improv this also means the exact same thing! It is very easy to get lost in an improv scene due to excitement, the fun and enjoyment that we forget that we do not have to speak every single minute. Sometimes there is something that can be a lot more effective – not speaking at all!
So, how do you start to incorporate this into scenes? Well there is a pretty easy rule that you can start to use in rehearsals – whenever you are walking – do not speak! Do rehearsals where you have to walk at points in the scene to get used to doing it. Also you could practise by limiting how many words each person can say in each scene and tell them to use it wisely.
Also after you say something, with the same facial expression, look to the audience – it will create great humour and will also again put another level into the performance. It may sound like a really simple thing but the impact is really effective.