How to improve communication skills in short time?

• Immerse Yourself. One of the most important things to do is to practise not only your listening, reading and writing skills but also your speaking skills. 
• For say you are trying to improve your conversation in a particular language such as English, then:-
• Watch English Films/Series.
• Read English Magazines or Books. 
• Listen to English Music.

It will not only improve your understanding of the language but also improve your vocabulary and enhance your general knowledge.

Interesting question and interesting answers.

A quick google search on communication skills gave me this: "the ability to convey or share ideas and feelings effectively." Note the word "effectively".

Clearly, "communication skill" is not tied to a single language.

Regardless of the language, improve your vocabulary. 
Always think before you speak. Do not do both at the same time as it will cause stammering.
Be precise and to the point.
Be confident.
Lastly, to your disappointment, it will take time just like a plant needs its time to grow into a tree. So don't rush.

Good luck!

First, decide what you want to communicate and to whom you want to convey.

Second, if you want to communicate or discuss a particular topic to a group of persons/one to one interaction follow these steps

collect as many information as possible related to the topic you want to communicate.

Jot down the relevant key points which help you to make the opposite end to understand what you want to convey.

Use simple words/terms, which is understandable by the majority of the people.

Try to correlate the things interestingly related to the topic.

Make your communication interactive so that the opposite end is always curious/eager to know what you want to convey.

Finally, do not drag too much.