Create a .gitignore file in your home directory. For example:
# Compiled source #
###################
*.com
*.class
*.dll
*.exe
*.o
*.so
# Packages #
############
# it's better to unpack these files and commit the raw source
# git has its own built in compression methods
*.7z
*.dmg
*.gz
*.iso
*.jar
*.rar
*.tar
*.zip
# Logs and databases #
######################
*.log
*.sql
*.sqlite
# OS generated files #
######################
.DS_Store
.DS_Store?
._*
.Spotlight-V100
.Trashes
ehthumbs.db
Thumbs.db
.classpath
.project
.settings/
# Emacs
*.*#
*~
Then run this command to set it as the ignore file to use globally.
$ git config --global core.excludesfile ~/.gitignore