Practice by itself is not enough. Getting feedback from your peers, advisers and professors on your talk is a great way to improve your it. However getting the right feedback is not as easy as one might think.
Before giving a talk at a conference, some of us at my research group rehearse in front of our peers and sometimes in front of our advisers. After the rehearsal we spend some time giving feedback and discussing it. The idea behind this feedback session is that the audience and our peers have a similar foundation knowledge and thus you are able to anticipate many of the audience's concerns and questions. Rehearsing in front of your peers and adviser also helps you to spot content errors on your presentation's visuals. However, before you rehearse in front of other people, you should have already practiced on your own, otherwise the feedback is not as useful as it can be.
The problem of asking for feedback is to get people to tell you what they really think. So before you start your test talk, tell me that only their most honest positive feedback will help you. It happened to me last year. I rehearsed in front of two very smart guys, M. and A. Although I had frequently rehearsed in front of A., I hadn't do it in front of M.. So I told him, "M., only your brutal honesty will help me". He nodded and I started. After I finished and we were discussing the feedback, M. told me "I don't like that blank slide!", and following that he said "You told me to be brutal!". I thanked him for that. We discussed why the blank slide was not appropriate and moved on. Then, we got to another point, something content-related. M. asked me why my Ansatz would work, and suddenly A. said: "Yeah, why? I have never understood it." I answered their questions, but I was left with a strange feeling on why A. hadn't asked me about this issue before. After all, he had heard similar talks where this point was mentioned. My guess is that he felt more confident asking now that M. had the same question. I was glad I had M. on board and that I had explained the kind of feedback I needed.
If you can, try to gather as many people as you can for your feedback session and explain what you expect from them and ask them to write down their opinion, suggestions, comments and questions on a piece of paper. But asking for people about their real opinion is not enough. I have found useful that somebody registers the time I take on the different sections of my talk. This helps me to keep track of time when I'm on stage. After you are done, let each person give you his or her feedback and discuss it. Finally gather their notes and adjust your presentation and visuals accordingly. I have found that it is impossible or inappropriate to take all the positive feedback into account. But I do listen to my adviser, after all she's more experienced than me.