Read up on the company and know what is involved and expected
Not hard to get a get a job here they are desperate for talent.
Do some company research - you can find it all on their website.
Look at who Aldi are and some stats to do with the company. Research why they are different from the other grocery stores, what they do that is environmentally friendly and contributes to the community. Eg. they don't use generic plastic bags but you can be reusable ones, they donate food to community organisations etc.
Then list out some things about yourself, why you want to work there, what you can bring to the company and why they should hire you, they may even ask you to share about a weakness of yours.
Lastly, practice your money maths! They will ask you a couple of maths questions because you have to manually calculate change at the registers. Questions like 'If a customer buys groceries that come to a total of $18.95 and they hand you a $50 note, what would the change be?'.
They asked me generic questions, most of which were written in the online form - should be easy just be yourself.