What is a good theme to talk about for an oral presentation on Much Ado About Nothing?
I guess one thing you need to think through carefully is what theme attracts you most - you must always pick a topic that you are enthusiastic about or that you are interested in, otherwise you will bore yourself as well as your audience.
One theme in this play that particularly interests me is that of deception. Think of the large number of deceptions that make up so much of the plot - for example, the gulling of Don Pedro and Claudio which sets the stage for Hero's disgrace, and then the pretense of her death which paves the way for her happy ending with Claudio. Then of course there are less serious deceptions, such as the way that Beatrice and Benedick are tricked into falling in love with each other. What is interesting to focus on then is deceit and how in some cases it is used for evil purposes and in other cases it is used for good.
This theme of deception is also something that is deliberately "muddied" or confused in the play. Consider the masque ball when Beatrice and Benedick are courting each other sarcastically. Are they aware of the identity of the other? If so, they seem to remain wilfully ignorant, playing along with the deception. It seems overall in the play that deceit is actually just a means to an end and a way in which characters are able to rise socially. You should therefore think about to what extent characters are deceived and also, crucially, to what extent they allow themselves to be deceived.