It depends on the morphology and the lexical category of the word.
If the word is suffixed, it will generally bear stress on its first syllable.This concerns words with grammatical suffixes (like Peachey's examples with -ing and -ed), but also lexical suffixes.
In general, stress is found on the first syllable, except :
- prefixed words that are not nouns (so mainly verbs, adjectives, and adverbs) : conCERN, rePEAT, unFAIR, etc. (words that are both nouns and verbs can behave differently according to their category, ex : REcord (n) / reCORD (v.) )
- words with some specific endings (generally borrowed from French) : -ade, -ese, -eur/euse, -aire, -que, -sce, -ette, -ee, -ier, etc.
- dissyllabic verbs in -Vte (where V stands for "vowel", so : -ate, -ite, etc.)
And themax : there ARE rules in English stress :)