If the form is based on a query or recordset it's easy. If not, it may be worth making the table a query by going to the 'RecordSource' property and clicking on the ... beside the name of the table. This will ask if you want to base the form on a query. Say YES and in the query builder pull all the relevant fields to the grid.
In the grid column you want sorted click in the 'Sort' row and set the option to either Ascending or descending as required. Usually I set this one, for dates, on descending as I would want the records to list from the most recent date backwards.
This method does not require any further action by the user and will always show the records sorted when the form is opened.
Dave E