No misdemeanor and won't affect your green card process. The most serious situation is another party has severe body injury in the accident.
2 我应该请律师么?
The ambulance was called on service? Do you have any real property and othher investments such as CD, stock, mutual funds?
3 我应该怎么准备?比如,我是不是该找到对方的车,拍个照片证明其实不严重什么的,还有别的什么我可以做的么?
Nothing you can do now. Gathering information is the first priority you should do. The most importance is the police report.
come back to ask if you get the police report