As romper wrote, you should be comfortable with discussing your topic and be well prepared in terms of the topic you are speaking about. Be attentive to your audience, engage them. At times try to use a little humor, it can go a long way in terms of getting people interested and having them pay attention to you. Eye contact matters and body language is a big factor as well. Be "Italian" when you speak, as in speak with your body too. Of course you do not want to move around too much but movement is important.
Prepare by speaking out loud when you are by yourself and be confident. Know your audience and prepare your speach for them. Believing in what you say is the most important thing in my opinion though. Your tone of voice is also a factor. If you are passionate of what you speak about, success is yours! Cheers and all the best!