There are a few English prefixes and suffixes that are an especially common source of pronunciation errors, mostly because they would be pronounced differently if their position in a word were different. Note: Pronunciation is given in British English.
-ful is pronounced /fl/; for example “awful” /ˈɔːfl/ (aw-fl), “skilful” /ˈskɪlfl/ (skil-fl). The suffix “-ful” is often mispronounced by foreigners as “full” (rhyming with “bull”) and also often misspelled with a double “l”.
-able is pronounced /əbl/; for example “noticeable” /ˈnəʊtɪsəbl/ (noh-tis-ə-bl), “doable” /ˈduːəbl/ (doo-ə-bl). Learners of English often mispronounce it as “able” /ˈeɪbl/ (ey-bl).
-age is pronounced /ɪdʒ/ (idzh); for example “village” /ˈvɪlɪdʒ/ (vil-idzh), “mortgage” /ˈmɔːɡɪdʒ/ (maw-gidzh).
-land is pronounced as /lənd/ in all names of countries, for example England, Finland, Holland, Iceland etc. Other nouns of the form “somethingland” are usually pronounced as “something land”, for example “grassland” /ˈɡrɑːslænd/ (graas-lænd), and similarly marshland, swampland, dreamland, wonderland, etc. The only four exceptions I am aware of in which “land” is pronounced the same as in the names of countries (i.e. /lənd/) are highland, lowland, dryland, and moorland.
-ical is pronounced /ɪkl/ (ikl); this itself causes little trouble, but the problem is that once you add the suffix “-ical” to a word, the stress moves to the last syllable before “-ical” (i.e. to the third syllable from the end). For example, “economy” is pronounced (in British English) /ɪˈkɒnəmi/ (ih-kon-ə-mee), whereas “economical” is pronounced /ˌiːkəˈnɒmɪkl/ (ee-kə-nom-ikl); “technology” is pronounced /tekˈnɒlədʒi/ (tek-nol-ə-dzhee), but “technological” is pronounced /ˌteknəˈlɒdʒɪkl/ (tek-nə-lodzh-ikl).
auto- is pronounced /ˌɔːtə/ (aw-tə); for example “autobiography” /ˌɔːtəbaɪˈɒɡrəfi/ (aw-tə-baay-ogg-rə-fee). The letter combination “au” is pronounced as /ɔː/ (aw) in general.
when it is a prefix, “de-” is pronounced /dɪ
/ or /diː
/; for example “decrease” /dɪˈkriːs
) resp. /ˈdiːkriːs
-krees) depending on whether it is a verb or a noun
re- when it is a prefix, it is pronounced as /re/ when it is stressed and as /rɪ/ (ri) when it is not; for example “to record something” is pronounced /rɪˈkɔːd/ (ri-kaw’d), “a record” is pronounced /ˈrekɔːd/ (re-kaw’d); see the link above for other words that change meaning depending on stress position.
in-, im-, un- are pronounced /ɪn/, /ɪm/, /ʌn/ and are not stressed (they sometimes carry a secondary stress). The important thing to remember is that they don’t influence the stress position in the word they modify; for example “incorrect” /ˌɪnkəˈrekt/ (in-kə-rekt), “impossible” /ɪmˈpɒsɪbl/ (im-pos-ibl), “unnecessary” /ʌnˈnesəsəri/ (ʌn-nes-ə-sə-ree).
micro- is pronounced /ˌmaɪkrəʊ/ (maay-kroh); for example “microbiology” /ˌmaɪkrəʊbaɪˈɒlədʒi/ (maay-kroh-baay-oll-ə-dzhee), “microgram” /ˈmaɪkrəʊɡræm (maay-kroh-græm). Notice, however, that “microscope” is pronounced /ˈmaɪkrəskəʊp/ (maay-krə-skoh’p), with “krə” instead of “kroh”.
pre- as a prefix is not stressed and is pronounced /prɪ/ (pri) or /priː/ (pree); for example “pretend” /prɪˈtend/ (pri-tend), “presuppose” /ˌpriːsəˈpəʊz/ (pree-sə-poh’z).
pro- as a prefix is not stressed and is pronounced /prə/; for example “proliferate” /prəˈlɪfəreɪt/ (prə-lif-ə-reyt), “propose” /prəˈpəʊz/ (prə-poh’z).
tri- meaning “three” is pronounced /traɪ/ (traay); for example “tricycle” /ˈtraɪsɪkl/ (traay-si-kl), “tripod” /ˈtraɪpɒd/ (traay-pod).