Praise be to Allah.
The Sunnah is that the imaam should stand in front of the other worshippers, if they are two or more, and no one should stand beside the imaam except in cases of absolute necessity, such as when the mosque is full and he can find nowhere to stand except beside the imaam, in which case there is nothing wrong with it. If there are only two other people and they have to stand beside the imaam, then one should stand to his right and the other to his left. They should not both stand to his right, as was originally prescribed; this was aborgated and the rule now is that they should both stand behind the imaam.
Many ordinary peple nowadays think that if two men need to stand with the imaam, they should both be on his right. There is no basis for this idea, but if there is only one man, he should stand only to the right of the imaam, nowhere else.