In case anyone wants to take issue with the way I spelled "traveled" in a recent post, here's the rule I learned in elementary school (don't ask me how I remember it) about doubling the final consonant of a word before adding a suffix: If the consonant is single, and the emphasis is on the last syllable, AND the quality of the last syllable is "long", the consonant is doubled before adding a suffix; not otherwise.
The long vowels are found in "heat", "hate", "hope", "foot", "hoot" and, I think, "hawk". The short vowels are "hit", "pet", "hat", "hot" and "hut". The twelfth English vowel, schwa is short, but doesn't come in for doubling because by definition it never has the emphasis.
Some examples:
"Hot" becomes "hotter" because the emphasis is on the ultimate syllable (its only syllable is the last one, of course) and the vowel is short. Likewise "besotted".
"Market" isn't doubled, even though the ultimate syllable is short, because the emphasis is on the penult: "marketed", "marketing". Likewise "customize", "bedeviled" and "opening".
"Touch" emphasizes the ultimate and the vowel is short, but it isn't doubled (to something like "touchhing" or "touchched") because it ends in multiple consonants. Likewise "hacking", "crutched", "commander" etc.
"Rude" becomes "ruder", not doubled, because even though the emphasis is on the ultimate, the vowel is long. Likewise "eloping".
This leads to some disagreement with the standard dictionaries. They think I should write "travelled", for example, and some of them also "cancelled", though I insist on spelling them with an undoubled 'l' because the emphasis is on the penult. They also want me to write "controlled", while I stick to "controled" because the final syllable is long. (I suppose phoneticians could argue that the 'o' that comes before 'l' is modified and no longer truly long; I can't feel it.)
And then there's "kidnapped". I spell it with a doubled 'p' despite the fact that the emphasis is on the penult; I just can't bring myself to write "kidnaped". I comfort myself with the thought "kidnap" is actually a compound word, that "nap" is actually the root. It may even be true.