Consistently delivering your best isn't easy because many factors affect your performance that aren't in your control. Yet performing at a high level more often than not is a difference maker not only for you, but also for those you work with, lead, or work for.
One way you can leverage what you have control over is to identify your keys to success. What do you tend to think, feel, do, etc. when you are performing at your best? Profile out a few standout performances you've had and look for these patterns.
Once you know your keys to success you can use them to your advantage to put yourself in the best position to perform at your best. It may not always be easy to put them into action, but at least you will have a clear idea of what your road to success looks like.