* Avoiding hardcoding numbers, making input cells a certain color, etc.
* Knowing the all powerful F4 key that alternates between A1, $A$1, $A1, and A$1 (and knowing what each of these mean)
* Inserting blank lines above and below a summed range and including those rows inside of the sum formula (prevents formula from breaking if you move rows around)
Other than that you can do a lot of productive things with a combination of index/match and dynamic named ranges via offset formula.