What is the rule for words ending in el or le?

There is no hard and fast rule but -le is much more common than -el.

That is true, but there are also some grammatical guidelines.
1. Verbs (action words) have the -le spelling (fizzle, fumble), so do nouns (table, angle) and adjectives (acceptable, deductible)

2. Nouns can also be spelled with -el or -il (trowel, shovel, devil )
3. Words that end with -ile are usually adjectives (fragile, agile)
4. Words that end in -al are generally nouns or adjectives (general, carnal, economical, aerial)
4. Exceptions: Very rarely, -ol is also used (capitol)

-le is usually preceded by a letter with a 'stick' or 'tail' (part of the letter reaching high or low), such as table, angle, whereas -al and -el are usually preceded by a letter without a stick or tail: camel, towel, aerial, local.

See http://thespellingblog.blogspot.com/2009/02/spelling-words-ending-with-le-el-and-al.html