Q:

working with .git/info/exclude too late

I usually do this:
git init
git add . 
git commit . 

And then I realize that it's about to add my nbproject directory, which I want excluded/ignored.  Sometimes, I even check in this directory.  Had I added it to .git/info/exclude before running git add.,  everything works fine (it's excluded).  
So then I modify .git/info/exclude and then it's too late.  git no longer respects changes to .git/info/exclude. 
So the questions are:

How can I get git to take up the changes in the exclude file in the checkin? ( I tried running git add .  again, which doesn't help)
Let's say I check in a directory (or file) that I want excluded.  What is the least number of steps to get to the state I want (with the file excluded).  

A:

To remove a file that you have added but not committed, use a command like this:
git rm --cached file.to.remove

This will remove the file from the index, but not touch the file on disk. 
To remove a file (or files) from the most recent commit, use the above git rm --cached command followed by git commit --amend.