Know and Do ... Yourself, Your Job

Know yourself - this is ever-changing.  Your knowledge, experience, perspective, maturity, motivations and priorities will not be stagnant. They will evolve, and you need to track and account for that evolution.

This is further affected when you are in a direct leadership role, responsible for others.  Whether as a parent-leader or work-leader, this will demand investment in gauging strengths and weakness perpetually. And, if necessary, seeking external inputs.

Know your job - for some this is a task in and of itself as not always is everything neatly laid out at work. So it is on you to establish clarity, learn the parameters, understand what is up to you and what is not your decison. 

Unfortunately, some don't quite know their job (or what constitutes excellence) or are uncomfortable seeking clarity.

Do your job - the simplicity of doing what you are supposed to consistently do will almost always earn you respect, credibility and confidence from your peers and seniors.  Producing quality products, listening to what your told, delivering on requests, being available, having a positive attitude, and following up to ensure you are on track are basic traits that will resonate positively.

To the best of your ability - two aspects: what are your inherent and developed abilities and what is "the best?" Tied to knowing yourself, leverage those abilities while keeping them fresh. Do not stagnate, do not become complacent. Challenge yourself to expand abilities. And who knows what your best is ... you do. And you also decide whether that is what you are doing.  Others will give their views, but you know - so bring it. And if someones says you can do better, believe it and bring more (don't fight it or argue you can't).