failed to push some refs to github

In the event that the github repo is pushed with new changes and your local repo doesn't have that changes this blunder happens for this you could utilize:

git pull -rebase

git push

The full syntax is:

git pull --rebase origin master

git push origin master

For pushing, I would recommend you to use -u option:

git push -u origin master

That would establish a tracking relationship between your local master branch and its upstream branch.