Mock trials are just practice trials that you can use to help you learn how to present your case. While the primary use of them is to learn how to conduct a trial they are also invaluable for practicing lawyers to help them to prepare for trial. There is no such thing as too much practice and even experience lawyers can benefit from it.
All lawyers are familiar with mock trials they are used at law school to help them learn how to present a case. Mock trials are also valuable for practicing lawyers as way to help them prepare the case they are going to present to the jury. It is always a good idea to practice beforehand and have somebody critique your performance. Lawyers also use mock trials to test different strategies so they can decide on which will be the best to approach to use at trial. This way they will be ready to when the time comes to present the best possible case.
Obviously if you are going to have a mock trial you are going to need somebody to fill the role of the required participants. You will need an opposing attorney, a judge, a jury and witnesses. It is unlikely that you are going to have any of these floating around your law firm. Therefore you will likely want to use a consulting company that can provide you with the other required participants. They will be able to provide an experience attorney for you to go against as well as somebody to be a judge. They may also provide you with a jury and witnesses if necessary for you to prepare your case.
You are probably also going to want to have somebody there who can critique your performance so that you can figure out where you can improve. Most consultants can also provide this. The person who does this will need to be an experienced trial lawyer who is able to offer you advice on what you did well and where you have room for improvement. You will also likely want to video tape the proceedings so that you can critique your own performance as well.
Depending on how many people are involved it can get pretty expensive to run a mock trial, especially if it is a complex case and you are trying out several different trial strategies. In many cases it won't make a lot of sense to go to this much expense. However even if it is just a simple case you may want to do a run through with another lawyer in your office just so that you can get a feel for the strategy that you are going to use. Obviously the level of preparation that you are going to need to put into the trial will depend largely on what is at stake.