Random sampling, stratified sampling, cluster sampling, etc. Random sampling is the most commonly used method, and its principle is to ensure the representativeness and reliability of samples by random sampling. Stratified sampling is to divide the population into several layers according to certain characteristics, and then randomly sample at each layer to ensure the representativeness and diversity of the samples. Cluster sampling is to divide the population into several groups according to certain characteristics, and then select all the samples in each group to ensure the representativeness and integrity of the samples. These methods are widely used in preschool education and scientific research, and can help researchers obtain reliable data and conclusions.