GA /t,d/ are elided in the coda when occurring between consonants. For instance, /t/ and /d/ are deleted in postcard, facts, walked back, windpipe, finds, gunned down, but not of course in actress and laundry, where they occur in the onset of the syllable.
These are some constraints on the preceding as well as the following consonant:
If the preceding consonant is /r/, there is no elision of either /t/ or /d/, as in heartbeat, cardboard. If the preceding consonant is /n/ or /l/, /d/-elision is common, but /t/-elision is not. Compare felt bad, stuntman, and cents, where /t/ is normally retained and realized as [t͜ʔ], with held back, landmark, sends, where /d/ is readily elided.
If the following consonant is /r,j,w,h/, elision is less likely, as in left right away, last year, last week, guesthouse, send Ronnie, old yachtsman, cold water, build houses.
The elision of /t/ in disyllabic contractions with /nt/ (not) is a special case: (it) isn’t clear, (he) doesn’t know, isn’t it, doesn’t she. Such an elision may also occur in monosyllabic contractions like (I) don’t like it, (I) don’t have one, but not when the contracted monosyllabic form is accented. So we would expect I ˈcan’t ˈdo it to differ from I ˈcan do it, i.e. [aɪ ˈkæ̃ʔ ˈduːɪʔ] vs [aɪ ˈkæ̃n ˈduːɪʔ], much like they’d spent the night there [ðeɪd ˈspɛ̃ʔ ðə ˈnaɪʔ ðɛr] differs from they’d spend the night there [ðeɪd ˈspɛ̃n̪ ðə ˈnaɪʔ ðɛr].
In nonstandard speech, final -Ct and -Cd clusters are frequently reduced to single -C, so that bold, past, next, left may be pronounced /boʊl, pæs, nɛks, lɛf/, even before a vowel or silence. In the standard language, this type of reduction may occasionally be heard in unaccented syllables, as in England, island, Egypt, perfect, though not in /nt/ clusters, as in different [ˈdɪfrə̃ʔ].
Try to practice /t,d/-elision between consonants, except before /rj,w,/ and /h/, as in fast race, last year, wristwatch, guesthouse, goldrush, second year, old wine, blind horse.
One further context where /t/ should not be elided is after /n/ and /l/, as in went back, pointless, salt mine, hints. In words like facts, texts, sends, winds, postcard, handbook, /t,d/-elision is the rule.
Here are some further examples to practice /t,d/-elision: costly, perfectly, soft palate, act two, windshield, standpoint, restless, lists.