Deploying a branch that’s not called master to Heroku (or pushing to a different branch name on remote in general)? Remembering to prefix the remote’s branch name with the local one might save you some confusion.
$ git push heroku my_branch:master
Where heroku is the remote, my_branch is the local branch name, and master is the remote branch name. Hopefully, I’ll get it right on the first try too, one day.