Some times those existing files don't ignore themselves...
(Well, I think it's pretty much all the time.)
Add this to your
~/.aliases dot file:
alias gig="git rm -r --cached . && git add . && git commit -m $*"
(Taken from this <a href="http://stackoverflow.com/questions/1139762/gitignore-file-not-ignoring">Stackoverflow post</a>.)
Then use it with the following command:
gig "Ignoring .DS_Store"