Keep it simple. A lot of people want to tell their life story at sentencing. As with anyone else, a judge is eventually going to tune out someone who just talks endlessly, and they may miss what is really important. As best as possible, just get to the point.
Don't try to get sympathy from the judge. Don't cry unless you really cannot help it. Crying usually makes judges mad because it appears that you are trying to persuade them with emotion. If you truly can't help it, the judge will probably see that. Don't have your children come up to speak, and preferably don't have them in the courtroom at all, particularly if they are very young. Judges get very angry when it appears to them a defendant is trying to use their children to get sympathy from the judge. They also usually think defendants are at best irresponsible if they bring their children in to see them sentenced. Don't where a uniform. If you happen to be in the military or some other uniformed job, wearing a uniform again appears to a judge to be an attempt to influence the judge. I have seen this with military and firefighters and I'm sure it has been tried and failed by other uniformed persons. Simply put, the judge is not going to have sympathy for you for anything you try to do to get sympathy.
The heart of what every judge wants to hear at sentencing is: what happened then, and what's different now. What happened then is usually easy: "I was drunk" "I was on drugs" "I was having a horrible day" "I really needed money", etc., the tricky part is what's different now. For example, a lot of people tell the judge they were on drugs at the time, but they are not now. That isn't good enough! Why aren't you on drugs now? What lead you to drugs in the first place? What has changed that will make sure you don't use drugs again? Quitting drugs because you are facing criminal charges is not going to impress a judge. Know what your motivation is to quit drugs for the rest of your life. If what happened then is about financial problems, or stress, or emotional issues like a death in the family, these are all issues that can happen again, so what's different that the next time you are in that situation you won't commit another crime? If you have a criminal record before this conviction, it is especially important that you can explain what has changed; arguments like you want to be there for your kids won't fly unless you can explain why you weren't thinking of that when this crime occurred. There is no guide to tell you how to answer the what's different now question, it's something you have to figure out and critically ask yourself (or better yet have someone else evaluate it and ask) is that really a reason you would not do it again?
What sentence you receive is still going to depend heavily on a number of factors including: what crime you were convicted of, your criminal history, the facts of your case, the impact of your case on others, and, unfortunately, what "message" the court wants to send to the general public with your sentence. However, a good statement at sentencing can make a significant difference in many cases, and a bad statement at sentencing can make a difference in nearly all cases.