Elision
As I have mentioned, a native speaker's aim in connecting words is maximum ease and efficiency of tongue movement when getting our message across. In minimizing our efforts, we weaken our articulation. If articulation is weakened too much, the sound may disappear altogether, a process known as elision. It is the vowels from unstressed syllables which are the first to be elided in non-precise pronunciation.
Common sound deletions
A syllable containing the unstressed "schwa" is often lost. For example,
int(e)rest,
sim(i)lar,
lib(a)ry,
diff(e)rent,
t(o)night.
/ t / and / d /
With consonants, it is / t / and / d / which are most commonly elided, especially when they appear in a consonant cluster. For example,
chris(t)mas
san(d)wich
The same process can occur across word boundaries, for example,
mus(t) be
the firs(t) three
you an(d) me
we stopp(ed) for lunch