voice recognition issues

Hey - I'm a newbie and I've never had a voice recognition system in any of my cars before. It's great in theory, but I'm finding that it doesn't understand over half of what I'm saying, which is particularly irksome when I'm trying to make a phone call to someone I KNOW is in my phone book (like my daughter) and no matter how I say her name it either insists she doesn't exist or offers me a list of people whose names don't sound a thing like hers! (This is just one example.) Any advice?