At meetings, decide what you want, state it openly, and listen carefully to what others have to say. Making the first move gives you the upper hand. Don't feel embarrassed about putting your ideas forward. You'll be noticed more than if you skulk in the corner. The more you do it, the more others will begin to look to you for your opinion.
Image is everything.
Look confident by walking tall and dressing appropriately. Smiles, handshakes and a firm gaze can do wonders for how others see you. Don't confuse assertiveness with aggression or showing off. Think whether people you know would like to work with someone acting the way you act. Seeing yourself from the outside might make you cringe, but will stop you from acting like an idiot.