I have worked with and for a lot of startups here is what annoys me the most:
Not trusting the people you hired. If you hired someone to do X, and you have 0 experience in X, then shut up and listen to the guy you hired! If you don't trust the guy then hire someone you can trust. You don't have to follow blindly, but you do need to consider what others are telling you.
Do not expect your employees to put in as much effort as you. This is your baby, this is your project, you can not expect your employees to throw in as many hours as you do. You can not get upset or punish your employees for not putting in as many hours as you do. If you want them to put in crazy hours give them incentive to do so. If you want them to be passionate about this project then (back to point one) treat them like they are part of shaping the business. Also, praise your employees(NOT yourself) when you see they are working hard for your startup to get off the ground. I've seen too many startup founders pat themselves on the back while wagging a finger at their employees for not working as hard as them.
Create a positive environment, if your turnover rate is too high then YOU are doing something wrong. Yes a start up is stressful, but do not take it out on your workers. You may think it's cheaper to constantly rotate through employees but it is not in the long term. You have to constantly bring these people up to speed, documents get lost, clients get confused, the atmosphere gets tense (all bad things for a successful business). You don't have to be (and shouldn't be) everyones friend, but you do not want to be everyones enemy.
Be organized, start a system for keeping things organized, teach everyone that system. Have your vision and instructions be as clear as possible, be available to answer questions. Things like a consistent tone of voice and "personality" for the company are important if you want to look like you have your shit together.
Clean and organized website with a nice and consistent look. You'd be surprised how many people don't get that. Worked with a Tech startup with a garbage website, looked ugly, horrible to navigate! Seriously hire someone with some design sense when you make your website, just because they know their way around a computer doesn't mean they can make a website that looks good or is in any way intuitive. Any idiot should be able to easily navigate your website and understand who and what you are.