Here is my current PS1:
$ echo $PS1
\[\e]0;\w\a\]\n\[\e[32m\]\u@\h \[\e[33m\]\w\[\e[0m\]\n\$
I have installed git bash completion and it isn't showing the current branch in my command prompt. I think this needs to be edited but I've got no idea what to change to make it show the current branch. Note that I like the colors and general structure (i.e. with $ on its own line), so I'd like to keep that if possible.
Modify the prompt string and add $(__git_ps1 " (%s)") somewhere.
For example, try typing this into Bash:
export PS1="\[\e]0;\w\a\]\n\[\e[32m\]\u@\h \[\e[33m\]\w\[\e[0m\]$(__git_ps1 ' (%s)')\n\$"
Once you find something you like, add that line to one of Bash's startup files, e.g. $HOME/.bashrc.
The source for git-prompt.sh is well-commented and worth browsing if you're curious about other options.
Note that you may have to manually source path/to/git-prompt.sh before this will work. If so, add this line to your config file as well, above the export PS1 bit.