I've been on three Soldier boards, one Soldier of the Month, one Soldier of the Quarter and one Brigade Soldier of the Quarter as a recorder. Here are some of the observations that I made on which people failed:
1. There's the basic one - Lack of subjects knowledge. Every battalion S-1 should send out an MOI with the board members and the subjects which will be covered on the board. Mostly all questions I have heard can be found in the studyguide. As a matter of fact, I gave a copy of the studyguide to my 1SG and he uses it for the boards now.
2. The biggest thing that people out here in the field fail to do is catch up on current events. Most board members will use the front page of CNN.com, so try to read that the day you go to the board. My battalion will give priority for the internet to soldiers who are going to the board.
3. Facing movements - be calm and listen to the commands, don't make a left face when he tells you to make a right face. Watch that your steps are the right distance, don't overstep.
4. Reporting - Salute first then speak, a lot of people speak when they are executing the salute, first put up the salute then speak.
5. Movement - Sit at the position of attention and try not to twitch too much and make sure you look the board member addressing you straight in the eyes and make sure you get their rank correct.
6. Speech - The biggest thing that I noticed of all the soldiers is that they speak too softly because they are either intimidated by the board members or they are not sure of themselves in their response. If you speak loud and firm, the board will definitely remember you and give you high marks. Don't use too many "uhms, ehhhs.." Be sure and be confident. Don't mix the ranks up..like First Sergeant Major...
7. Division songs or the Army song - Know them and sing them with pride and distinction.
8. The NCO Creed - The board president made one soldier do it at the start rather than the finish and he didn't know it so he was dismissed without being questioned. If you don't know the NCO creed by heart, don't bother attending the board.
9. Even though you are out in the field you can still find someone with an iron or a black marker. Make sure your LBV's buttons are colored black, your boots appear clean, your kevlar's chinstrap fits tight, and your kevlar cover is serviceable
Those are the things that I noticed from my three boards. They are all field boards so I can't give any info on boards back home till I go to them. I was the recorder also so I know how the scoring works, at least about my battalion. Every board member scores every soldier on appearance, reporting, etc. and their own subject areas on a scale of 1-5. Most likely they will give the first person, if he does a decent job straight 4s across the board, because they don't want to overscore or underscore the first person, because they might have a soldier doing better later on and they don't want to give them the same score if one did better. PT and weapons scores are important too. You can get 10 whole points if you get expert and above a 270 on your PT.
So I suggest you know your subjects, but if you choke at the board, be loud and confident about what you say and say you don't know the answer.
That's about all the advice I can give at this point, but if I come up with some new stuff, I'll definitely let you know.
By the way, if you ever want to try out for the Sergeant Audie Murphy board you have to be extremely efficient and confident about your subject materials or you will not be sent on to the next board. That board is the hardest board in the Army so you will have to be high speed on your knowledge and leading abilities. At the Sgt. Audie Murphy board they will more likely ask you situational questions as well as exact FM numbers, and regulations.
Good luck and keep studying.