DROP, SWAP and DOUBLE
Drop a silent 'e' at the end of the word, if the new ending begins with a vowel or a 'y'.
-     Hope + ing = hoping
-     Tape + ed = taped
-     Note + ed = noted
Swap a 'y' at the end of a word for an 'i', if the 'y' has a consonant in front of it, except if there is a double vowel.
-     Happy + ness = happiness  
-     Carry + ing = carrying.  It cannot become carriing, so keep the 'y' in this case.
Look at the vowel - if it has a long sound (alphabetic), just use one.  If it is a short sound, then double it. The additions to the words are added to a consonant immediately after the vowel.-     
-     Collar = short vowel sound
-     Polar  =  long (alphabetic) sound.
-     Begin = short vowel sound, so double the 'n' = beginning
-     Stop   = short vowel sound, so double the 'p' = stopping

The additions to these words are added when the consonant does not sit next to a vowel, therefore, leave the last consonant as single.

-    Watch = watch(ing)
-    Return = return(ed)

Also, look at the last three letters of the word in question.  If those three letters are consonant - vowel - consonant, then double the last letter of the word.   The exception here will be a word ending in 'x'.

-       Wet     =  wetter
-       Forgot = forgotten
-       Shop   = shopping / shopped
-       Travel  = traveller / travelling
-       Occur  = occurred
-       Begin  = beginner / beginning
-       Regret = regretted
-       Run      = running
​-       Cancel = cancelling / cancelled