1. Eye Contact
This is something that I admittedly struggle with on occasions and I'm sure that you probably do too. But if you make good eye contact you can appear trustworthy and decisive.
I have talked to people about shy people and what they might do and have shown them an example and their first reaction was that it is almost scary and creepy.
2. Do the Superman pose
What you are basically doing with this is that you are conning your brain into thinking that you are stronger and more confident that what you really are.
3. Dress well
Guys, I'm talking to you. How do you feel when you walk around in a cool suit with well polished shoes and tie or no tie? (I think ties are a waste of material but that is just my opinion and might get deported from this country if I say that any louder) I'm willing to bet that you feel more confident when you 'dress up.'
4. Speak slowly
In Toastmasters we are "told off" for using umms and has in our speeches. When you use this utterances in your sales presentations there are a couple of things that might happen. The listener might wonder if you know what you are talking about or secondly they might wonder if you are trustworthy or not. So slow down, think about what you saying and don't be afraid to pause if you can't think of the correct word. That small period of silence can be powerful.
5. Use hand gestures.
Have a look at the following video about The Rock Dwayne Johnson. In the video we see how The Rock uses his hands to come across as very charismatic.
Just watch the video. I can't explain it any better.