1. Just type in 1 in the first row and 2 in the second row.
2. Highlight the 2 cells.
3. Move you cursor to the bottom right corner of the highlighted cell, and your cursor will change to a cross.
4. Left click and hold when the cursor is a cross.
5. Drag down, and this will cause the cells you select to increment based on the scheme in the 2 highlighted cells.