Using The Fill Handle...

Quite possibly one of the most unknown and/or under-utilized feature in Excel is the fill handle (it's the small black square in the bottom right of the active cell (the square you're in)).

This little slice of heaven can save you so much time and energy. How many of you are still entering number sequences by hand? Something like this...
1
Enter or Arrow Down
2
Enter or Arrow Down
3
and so on...

Excel is secretly standing back thinking what an idiot we are for doing that. If only we'd use the fill handle, we'd be done already!

Next time try typing a "1" and then grabbing the fill handle by hovering over the little black square in the lower right corner until your mouse pointer turns in to a plus sign. Click the left mouse button and hold it as you drag down to where you want to be.

Your Auto Fill Options menu will pop up with several options to choose from (Note: these options change depending on the information you are working with. The Fill Months, Fill Days, etc. options are only available if the cell contains a date). If you want all cells to have the same number you can leave as is, or choose "Copy Cells" and all cells will stay the same as the first cell.

If you want to create a series (1, 2, 3...), you can choose "Fill Series" and the series continues through to the last highlighted cell. (Note: you can also achieve this by originally entering 1 and 2, then highlighting both cells and dragging down...this automatically puts the numbers in sequence).

Oh, but wait...it can do SO much more!

Excel will auto populate days, months, dates, etc... You can type in "Monday" and drag that fill handle down and it will automatically fill in all the days of the week! You can type in "January" and drag that puppy down and it will automatically fill in all the months of the year! And you can type in "12/1/12" and pull that bad boy down as far as you want and it will keep adding each date until you stop!

This also works horizontally!

If you go too far, no worries, just drag your fill handle up or left (depending on the direction of your text) and it will clear the contents of those cells!

Or maybe, you need to add some columns or rows in the middle of your information. Just select the cell where you want to insert extra rows or columns and drag right or down while holding the "Shift" key.

Your Auto Fill Options menu also has options to Fill Formatting Only which will copy the formatting of your previous cells without copying the information and Fill Without Formatting which will fill the cells with the next numerical number without the formatting previously used (i.e. dates will be converted back into a numeric value instead of looking like 12/1/12).

Totally Amazing, right? Such a great time saver for all future projects!