Tip: Are you a non-native English speaker? I have just finished creating a 
Web AppUnlike some languages in which one grapheme (one letter) corresponds to one phoneme (one sound), English uses a complicated (and largely irregular) spelling system in which most sounds are represented by groups of several letters.
Among all the irregularities, there are a few patterns in pronunciation that can be learned and this article describes the most common ones (ordered so that the groups I find the most relevant for a learner are written first). Note: the rules described here hold only if the respective group lies within one syllable. For example, “ee” is always pronounced /iː/, but not in “preemptive” /priˈemptɪv/ (pree-emp-tiv), simply because the syllables are “pre-emp-tive” (resp. “pre-emp-ti-ve” according to orthographic rules), not “preemp-tive”. Pronunciation is given in British English unless stated otherwise.
The list of groups
wh as in where, which is often taught to be pronounced just as /w/ (i.e. that “where” and “were”, “which” and “witch” sound the same). However, it is also quite common among British to pronounce it as /hw/, i.e with “h” as in here in front of “w”. (Rowan Atkinson is a good example of this kind of pronunciation.) Linguists also denote this sound by a separate symbol: /ʍ/. There are a couple of words in which it is the “w” is silent, not “h”, e.g. who, whole, whore (but not all that begin with “who” are of that kind, for example whorl, whoa are pronounced with silent “h”).
oo is mostly pronounced in two different ways: /uː/, as in fool, cool, or /ʊ/, as in book, look (the same sound as in put, full). There is no rule to decide which one is the correct one. It is sometimes pronounced also /ɔː/ when written as “oor”, as in door, floor, or /ʌ/ (as “u” in “but”): “blood” and “flood”.You can read much more about “oo” in my article about the long and short “oo” in English.
ow can be pronounced either /au/, as in cow, how, or /əu/ in British English resp. /ou/ in American English, as in low, snow. There is no rule dictating when to use which one; there are even 4 words that can be pronounced both ways with different meanings: bow, row, sow, mow.
ng is usually pronounced as /ŋ/, as in wrong, song (as if one were saying “g”, but instead of “puffing” air, just touch the upper palate). This is true even if it is followed by “ing”, for example singing /ˈsɪŋɪŋ/, longing /ˈlɒŋɪŋ/, or by “er” when it means a person doing something, for example singer /ˈsɪŋə(r)/, gunslinger /ˈɡʌnslɪŋə/. In other such cases, it is pronounced /ŋg/, for example longer (“more long”) /ˈlɒŋɡə/, strongest /strɒŋɡɪst/. It can also be /ŋk/ when followed by “st”, but there are only two such words: angst and amongst.
nk is pronounced /ŋk/, as in think, blink. It must be pronounced with the “k” at the end in order to be distinguished from “ng”! “Think” and “thing” don’t sound the same.
ch is mostly pronounced either as /k/, as in character, chord, or as /tʃ/, as in chicken, chest. Almost all words containing “chi” or “che” are pronounced with /tʃ/ (but notice “chiropractor” /ˈkaɪərəʊpræktə/ (kaay-roh-præk-tə) and “chemistry” /ˈkemɪstri/ (kem-ist-ree), but there’s no reliable rule for “cha”, “cho”, and “chu”. In some words of French origin, it is pronounced as /ʃ/ (sh), for example chef, chic.
ps is pronounced just as /s/ (p is silent), for example psychology, psalm.
eu is pronounced as /uː/ or /juː/ (yoo), as in neuter, leukaemia. The difference is mostly dialect-dependent; it doesn’t carry any difference in meaning (/uː/ is used mostly in British English and /juː/ in American English). Nevertheless, it is generally just /uː/ after “l” and “r”. Also notice that “neuron” is pronounced /ˈnjʊərɒn/ (nyoo-ə-ron) UK, /ˈnʊrɑːn/ (noo-raan) US.
au is pronounced as /ɔː/ (as “aw” in hawk), e.g. caution, aura.
th has two possible pronunciations: /θ/, as in think, author, and /ð/, as in that, although. There is no general rule to decide which one is the correct one.
sh is pronounced as /ʃ/, as in show, fish.
aw is pronounced as /ɔː/, as in hawk, paw.
ee is pronounced as /iː/, as in need, seen.
ur, er, and ir are usually pronounced /ɜː/ in the UK (a sound similar to long /ə/) and /ɝː/ in the US (just a long American /r/), as in curve, purge, herd, serve, bird, stir.
