What kind of gis project do you want to do? Generally give a direction, spatial database direction, remote sensing application or gps direction. If you are familiar with database and programming, I suggest choosing the direction of spatial database. You changed your major, and you may not know much about gis. The basic requirements of spatial database for gis are not particularly strict. Knowing more about arccatalog is not a big problem. Many people have done this, and it is easier to look up information. You can go online and have a look.