Do you have any tips for the promotion board?

Promotion boards are more about presence than knowledge. Everyone spends hours memorizing things to study, and they don't take into account that half the boards score is uniform and military bearing. You can answer all the questions correctly and not be recommended because of your bearing. However, you can miss most of the questions and still be recommended because of your presence and bearing. The board members know within the first minute whether or not you will pass.

Practice a mock board. Practice your bio. Know your creeds. Say these things out loud. Practice projecting your voice. Preparation is key to passing boards. It's immediately apparent to the board who did and did not practice.

Go in with a good attitude and be confident.

Be confident. Know whatever is on your study guide, but if you really don’t know, explain how you’d find it.
Know the NCO creed, be able to say it calmly. Have people interrupt you while you’re practicing it, so if you get flustered or stuck at the board, you’re used to rallying and picking back up.
Stay calm, be confident, know your stuff.

Be confident in your answers. Even if they are wrong answers. Also make sure your awards on your uniform match your ERB.

If it's voluntold, decline to go, or tell the president of the board you dont wish to be there.
If you do want to be promoted, obtain a copy of the memo and the governing regs/pams/FMs/policies of the subjects, and watch the news, read the paper for current events.
Study. Practice with peers. Have your supervisor prep you and go over your uniform with you.
Be able to identify and describe correct placement of everything on your uniform without looking at it.