1. EME /g/ and /k/ were lost in initial position before /n/: late 17th century.
2. Two allophones of ME /h/--the palatal fricative and the forceful velar fricative--were lost in most dialects (a) after vowels; (b) before /t/; and (c) in final position, except when the fricatives merged with EME /f/. [See also "The Middle English Consonant 'H'" and "Compensatory Lengthening of Vowels." ]
3. EME /l/ was lost (a) after low back vowels; and (b) before labial or velar consonants.
4. EME /r/ was lost before /s/ (a change beginning in ME). By the early 18th century, /r/ was regularly lost after back vowels. During the 18th century, /r/ was in general lost before consonants. [Note that in some American dialects, /r/ is retained in these positions in PDE.]
5. EME /t/, and sometimes /d/, tended to drop in consonant clusters involving /s/.
6. EME /w/ was lost before /r/ in initial position: 18th century.