I have cloned a git repository and then checked out a tag:
# git checkout 2.4.33 -b my_branch
This is OK, but when I try to run git pull<         
        
Try this
git checkout master
git pull origin master
Edit: For newer versions of Git, --set-upstream master has been deprecated, you should use --set-upstream-to instead:
git branch --set-upstream-to=origin/master master
As it prompted, you can just run:
git branch --set-upstream master origin/master
After that, you can simply run git pull to update your code.