i sometimes lack vocabulary while speaking in a presentation.

Usually it happens if there is no complete understanding of subject of presentation, leads to lack of confidence. Also while presetation, needs proper & specific words to stress the specific point, this will be obtained by regularly reading novels and using such words in day to day life. This will improve the communication skill.br /Further If we are expert in reading the audience mind & judge what is they are finding in presentation, & if the efforts made to produce the required, then the presentation is 100% successful.