Had a question like this in one of my startup forums, and this is what i answered:
Haven’t really worked on my own very ‘mature’ company but I’ve started a couple through infancy. So most of my thoughts will probably be on that phase. This is the stuff i tell myself.
Pick a team you can work with. I’ve learned that the most important part especially at the infancy of a startup is the team. Always always pick people you trust and can work with. At this stage all responsibilities fall on a couple/few and if one of those cogs doesn’t work right or doesn’t work right together, it’ll pretty much cripple the startup.
Respect your colleagues. Its an A Team of sorts. Just because that designer/sales/developer guy works less hours than you doesn’t mean hes not doing enough work and doesn’t deserve his cut. Arguing about percentages before a product/service release is just stupid. Everyone should be committed as you are. Never discount your colleague’s specializations just because you dont understand what they do.
Things might go a bit slow, and it’s sometimes unavoidable. Sometimes, depending on what you’re doing, you role might just get very idle. Sometimes we just need to wait for some other third party to validate and revert back on some deal/project. Sometimes, the developer just needs to implement some stuff before the next phase. Patience can be as important as pro-activeness. It doesn’t necessarily mean the startup is stalling. Don’t panic. List down what you can actually do, then decide if its viable. Else, wait.
A little project management goes a long way. Don’t just assign tasks over coffee and hope the other guys remember all the details crisply. Use tools like Asana, Trello(I personally dislike Trello, though), Jira. Whatever floats your boat. But a place where everyone can see what others are working on will reduce load on a centralized project manager and allow people to communicate better. Have standups where people update what they did since the previous standup and what they plan to do till the next one. This will improve drive and communication. In scrum agile methodology this is usually done daily but can be adapted depending on your startup. The goal is to make sure everyone doesn’t work in their own cell and not be aware of what your teammates are doing.
Drive and passion. Its very important to be able to self motivate. The probably wouldn’t be a boss to make sure you do work. Remind yourself what you want to achieve, what needs to be done. Break larger goals in smaller subgoals that can be completed and easily gauge where you are to achieving it. Celebrate achievements/milestones. Feel good doing what you do.