Select the cell or range of cells
Go to the Home tab
Click Wrap Text
Adjust the column width by dragging the column border
Adjust the row height by dragging the row border
Use Alt + Enter to insert a line break within a cell
Reduce the font size if needed
Change text alignment to fit better
Merge cells if appropriate
Use Shrink to Fit from Format Cells
Right-click the cell and choose Format Cells
Go to the Alignment tab
Check Shrink to Fit
Click OK