You basically have two options to prevent users from inputting text into empty cells. One option is to turn off the grid lines. Alternatively, you can hide unused columns and rows.

To turn off the grid lines, click the Microsoft Office button and click Excel Options. Click the Advanced tab. Under the section ‘Display options for this worksheet’, uncheck the Show gridlines option. Click OK.

To hide unused columns and rows, select the first unused column (or row). Press CTRL + SHIFT + Right Arrow, right click the selection and click Hide from the context menu.