Reading new words in English makes much trouble. There are few rules and many exceptions to them. Anyway, certain patterns can help you get it right in many cases. This post explains a rule to figure out how to read vowels in words you don't know.
Reading vowels: Diphthong and flat sounds.
Vowels are often read like diphthongs, the same way they are spelt in the alphabet, or for instance these words: make for A, these for E, like for I, phone for O, music for U.
Otherwise, they are read like flat sounds, the same way they are read in man for A, get for E, did for I, not for O, but for U.
Below there is a list of words split by syllables. Yo can see there how vowels at the end of syllables are read like diphthongs, whereas the rest are read like flat sounds.
Dipthong A: pla-ce, ca-se, ma-ke, ta-ke, sa-me, la-ter, pa-per, pla-te, ta-ble, Sta-tes
Flat A: and, back, can, had, that, man, hand, fact, ask, last, af-ter, mat-ter, as-sist, at-tach, ban-ner, man-ner, af-ford, ad-dress, ad-dittion
Dipthong E: re-ceive, be-fore, le-gal, the-se, re-port, se-rious, de-pend, re-pair, be-cause
Flat E: get, her, tell, then, well, when, yes, next, less, yet, get-ting, hel-lo, bel-ly, let-ter, mes-sage, bet-ter, ef-fect, sel-ler, yel-low
Dipthong I: li-ke, ti-me, li-fe, ni-ce, fi-ne, qui-te, kni-fe, I-reland, Chi-na, ti-ger
Flat I: did, him, his, think, this, will, with, thing, big, still, lit-tle, dif-ferent, sin-ce, kil-ler, win-ner, mir-ror, big-ger, bit-ter, vil-lage, din-ner
Dipthong O: o-ver, tho-se, ho-tel, ho-me, pho-ne, so-cial, no-tice, Ro-me, jo-ke, ho-pe
Flat O: from, got, not, long, front, wrong, lot, job, boss, shop, on-ly, of-fice, bot-tle, cof-fee, col-lege, hos-tel, poc-ket, hot-ter, Tom-my, com-pany
Dipthong U: u-se, stu-dent, mu-sic, U-nited, ru-les, hu-man, mu-te, cu-te, ru-de, U-niversity
Flat U: but, just, cup, much, must, stuff, lunch, cut, luck, duck, un-der, Dub-lin, bub-ble, but-ter, cur-ry, sum-mer, sub-ject, num-ber, Rus-sia
Although there are exceptions to this pattern, it is very reliable. It's the best way to figure out how to read vowels a word you don't know, therefore I would recommend you to master it.