Yes. These work well. Here are some more tips that have worked for me:

• If eye contact is really uncomfortable for you at first, you can look at the person's nose.
• With power postures, if you're ever in doubt, open yourself up. Open your arms, for example. This shows openness and confidence, which other people definitely pick up on.
• Deep breathing is another technique for instant confidence
• And remember that other people are more concerned about themselves than they are with you. There's less pressure than you think!