You can control column structure by changing your spreadsheet.
Use the first worksheet. When a new app is created from an existing spreadsheet, AppSheet will automatically configure the new app to use only the first worksheet of the spreadsheet, even if the spreadsheet contains more than one worksheet. Once the app has been created initially, you can configure your app to use other worksheets within the same spreadsheet, worksheets in other spreadsheets, or even other data sources entirely!
Avoid special characters in worksheet names. Microsoft Excel prohibits worksheet names from containing these seven special characters:
[(left square bracket),
](right square bracket),
?(question mark). Although permitted by AppSheet, it is best to avoid using these special characters in your worksheet name.
Just header & data, please. You could put almost any content in a spreadsheet, including charts, pictures, free form text, etc. However, if the data isn't obviously tabular, AppSheet will probably fail to identify it. Ideally, the first row should contain well-formatted column headers, and the remaining rows should contain only data. For maximum app performance, delete blank columns and rows.
Use well-formatted column headers and provide a data sample for column type deduction. When creating a new app, AppSheet will try to deduce the column types of your data by considering the well-formatted column headers and any existing data.
Use spreadsheet data validation rules where appropriate, as described in the article about dropdowns from worksheet validation rules.
If AppSheet still doesn't quite get the column structure right, you can tweak it in the app editor.