Since you have given a specific topic of Basic Communication Skills, your task is relatively simpler. Look up this site by doing a search for a PPT on Communication Skills. You are also welcome to visit my website
www.actspot.com and check the courses to get an overview of the subtopics under communication skills.
Now that you have a broad idea of the topics, decide on the topics that you think are relevant to the audience and that can be covered in the timeframe allotted to you. Ensure that there is a good flow and transition between the topics so that there is a logical build-up and synergy. Now, focus on the specifics to be covered under each submodule and pay attention to the examples and exercises that will reinforce the learning.
If using PPT, ensure that the PPT supplements the inputs you share and is not cluttered with information. Work out ways and means to engage the participants since it is not teaching but a training session. You will have to practice extensively to get a good grasp of your material as well as to become aware of areas of improvement. Don't hesitate to do mock presentations to friends or family to get their feedback and suggestions.
Remember, your confidence in yourself is the key to being a great trainer. You can be confident in your ability to deliver excellently only if you are confident about your preparation, your material, and your grasp over your subject.
Best wishes