Follow through, and deliver what you say you will do. Only start things that you know you can and will finish, and then finish them on time, and without complaining. If you don’t, you will end up with a reputation as a flake, and there is one thing that Hollywood is full of, and that no one can stand, and that is a flake. Don't make lame excuses. Never lie. A good agent or manager can usually smell a lie from a client, because we're trained in acting techniques just as you are, so don't lie. The only thing worse than a flake, is a flake who is also a liar.
Be organized, and write out daily, weekly, annual, and life time goals. The most productive and successful people make daily to do lists of goals that must be done that day. These goals should lead up to things that must be done for the week, month, year, and ultimately, that complete the big picture of what you intend to achieve in your life. If you do not write things down and act on them, you will most likely not achieve what you intend to do. The very act of writing things down is a magical act that helps force you to manifest what you set out to accomplish. Think it, write it, and do it. Create the reality you desire. Creation begins with transporting non physical thoughts and ideas in to a physical form. That first form is to write it out.
Know your craft. If you are a successful architect, you are going to know how to build a building or a home. You are going to know the latest technologies that can make your job easier. You will know the price of wood or steel, and you will know who just built the grandest home or building in the world. Similarly, If you want to be a model, actor, or musician, you are going to know the latest designers, or who won best picture for the Academy, or a Grammy. You are going to know Stanislavski, or voice diction, or how to walk a runway or pose for long periods of time without showing fatigue. You will know the buzz words in your industry, the tools of your trade, marketing materials, and you will have them.
I once met an actress, and the day after The Academy Awards, she could not name for me what film won best picture. A week later, she still could not tell me. If you show no concern or care about your peers in your industry, who have achieved what you intend to achieve, you should quit now. If you walk in to interview with an agent or manager, it will be in your best interest to impress them with your training, education, and personally acquired knowledge. No one will tell you that you know too much. Instead, they will want you around. But it is possible that people may say of some one behind their back, this person does not know what in the world they are doing, they are a waste of my time. Do not be that person. Be a master of your craft.