The fill handle is great for Months, Weekdays, Quarters, and Dates, but why won't it fill 1, 2, 3? This episode shows many workarounds. Also includes:
You can fill a series by using the Fill Handle
You can drag down or right
Filling months works automatically
Filling weekdays works automatically
Type in ALL CAPS to have the fill be all caps
Abbreviations work for months and weekdays
For years and quarters: 1Q-2016
Any word followed by a number works
Hold down Ctrl key to have 1 fill to 1 2 3
You can press Ctrl after you start dragging
Hold down Ctrl to copy dates instead of filling
Right-click and drag to fill weekdays or months or years