On the Job Preferences page, you get to select the areas you are most interested in gaining an apprenticeship or traineeship.

It is strongly recommended that you specify all three preferences and be as specific about the Industry Category and Industry Subcategory as you can be.

If you know exactly what Qualification you are shooting for, then specify that as well.

An Employer is more likely to favour someone whose preferences are the same as what they have to offer, so being specific has distinct advantages over being vague.