If you say crew performance is key, then I tell you a key is a precision object - get your measurements right. How to measure performance? By Performance Reports. It is not just a mandatory paperwork that the company asks for.
Performance Reports are for identifying strength and weakness of each individual crew. What is the point to keep it confidential? Correct, the comfort and easy life of the one reporting. Sorry, but there is nothing easy in evaluating a persons abilities, so do not take it easy. Make an effort to observe your crew over the period of time, takes notes of each good and bad that you see, and summarize it when it is time to write the performance report. Then create the setting to discuss with the individual crew.
Capitalize on talents, rather than on knowledge. Include competencies such as resilience, ability to take criticism, alienation to seafaring job and life.
Best if an individual performance report will become a personality biography of a crew.
Whom will I tell the truth? Those who put me under pressure, or those who I trust?

To top it, create department performance evaluations; an effective performance indicator.

Serenity Prayer
God grant me the serenity to accept the things I cannot change,
Courage to change the things I can,
And the wisdom to know the difference between those two.
- Reinhold Niebuhr (*1892-1971, American theologian)

...and since no choice, ergo, optimism is mandatory - Dr. h.c. Dirk Steffens
but
We have to articulate ourselves, otherwise we would be cows in the field
- Werner Herzog 1982

All crew always need a cool leader. Master onboard needs a cool leader from office. Office represents composure, reflection, action for a matured, classic-rooted, reliable leadership.

A steadfast fortress is our God - Martin Luther

Do not delay crew home allotments. Not by bank wire transfer times, currency exchange gains, company profit reasons like time deposits.
Do not refer crew training with a referral fee from training centers. Crew on leave sactifices their recharging period called leave, not to mention their personal money and time.
Do not allow contract extension when you have crew on vacation with no income. Then again, retention rate is not a marketing tool.
Do not jump to hasty conclusion for crew discipinary action. MLC's anti-bully rules are published but do not follow the populists bully finger pointing. Remember the weak have no lobby. Remember the being bullied may need relieve earlier than the bully.
Treat crew who leaves for whatever reason with respect. Remember you meet twice in live and trice in shipping.

For sure no crewing approach will ever be perfect, but the level of love and dedication counts.
You can go a long way when your aspirations are high - Richard Ford