like Lisa--my husband is my main assistant. though my nieces and nephews often assist me in studio shoots too. my husband is also a photographer and he's one of my models, so he almost always anticipates me and understands what I'm going for in a shoot. he's an air traffic controller, so his schedule is very flexible, which is also helpful.
my creative shoots are usually about four hours. it's invaluable to have someone assisting you who knows you well, knows how you work and how you shoot. my husband even knows more about my downloads than I do half the time. he's always logging into my account to check my stats, and he does all my payout requests and that stuff--I concentrate on the shooting/processing/uploading.
when I work events like concerts or film festivals, or awards ceremonies...stuff like that, I work alone. it's enough jumping through hoops with just me to worry about at those types of events without worrying about the logistics of having an assistant there with me.
Tyler-maybe part of the problem initially is that you just need to develop a closer rapport with your assistant and let them get to know you too. as someone said earlier, you could set things up so that you're forced to hand some of the shoot jobs over to the assistant and that way they'll learn how you work and you can step back and use your creative time, which presumably is why you've made the decision to work with an assistant at this point anyways :-)