The most common problem is the timeout issue which is caused by a low-value set to some php configurations. See here for more info
Make these values higher than default. Example:
- max_execution_time = 300
- max_input_time = 300
- upload_max_file_size = 256M
- post_max_size = 256M
- memory_limit = 256M
These values are not perfect and it depends on how large of an import you are making. So the bigger the import, the higher the numbers should be.