I'm planning to meet my potential employer and tell him the truth before they even begin the background check. I have a letter from my attorney that explains my case. Are there any other documents that I should be taking when I meet him? Will this conviction of simple assault snatch away my job offer? How do I maximize my chances of convincing my employer of hiring me in spite of this misdemeanor case. (I'm currently on F-1 Visa and the employers have offered to sponsor H1B for me).
Simple assault should not have any immigration consequences for you. An employer, however, is not obligated to give you a job, and may deny your application for any reason (non-discriminatory) or for no reason at all. If the potential employer is going to do a background check it is best to level with him. That does not guarantee you a job however.
Ask your lawyer what he or she needs. Often clients fail to really communicate with their counsel. Lawyers here cannot tell you what you need to hear from your own lawyer. There is no way to tell what your employer will do with your assault. Many won't care. Others may have a different concern. Legally, your employer should only take action against you, if the conviction is relevant to the job duties, e.g. assault for security guard, DUI with delivery person driver, etc. Check with an employment attorney.
I am sure your attorney who represented you for the criminal matter has advised you as to what you need to do to prepare for this interview. Aside from the letter from your attorney and your honest explanation of what occurred, there is little else you can do. Whether or not your potential employer will find this innocuous or a reason to not hire you is entirely within their discretion.