I hope you know how to set up your network. This post won't cover that topic and just goes straight to the settings of MPD.
I'm using Doid MPD Client to control MPD from my phone. I haven't tested any other MPD client yet but I guess they are similar to Doid MPD.
First of all bind your MPD to your internal IP or DNS by editing these lines in your mpd.conf:
bind_to_address "<your IP or DNS>"
You can also add a password:
password "<your password>@read,add,control,admin"
The options behind @ can be mix and matched the way you need them. Even multiple lines of the password setting are possible for different passwords with different options.
Don't forget to restart MPD after doing changes in mpd.conf.
The Droid MPD client is available in the Android Market: https://market.android.com/details?id=com.soreha.droidmpdclient
Just install it, configure the IP, port and password you've set up in your mpd.conf in the settings of Droid MPD client and enjoy a neat remote control for your music.