In Vim\'s normal mode:
as seen on VIM manual (section 03.1), you can use ge to go to the end of previous word
You may also want to do these to go to the space preceding a word (one character after ge: (both are only 2 keys)
The exception is when you are at the beginning of a line, in which case
Try ge:
ge Backward to the end of word [count] |inclusive|.
*gE*
gE Backward to the end of WORD [count] |inclusive|.
Unfortunately it's not a single key... but ge is what you're looking for, I think.