Before bringing your machine is single user mode
1)you inform other users logged in about the event using wall command.
2)If you are sharing a files using NFS protocol Make sure you disable network access to shared file systems using exportfs -ua.
3)Make sure no critical process such as backupjobs are running in background.
5)confirm the runlevel using runlevel command.
Here is a different way of doing it at system boot.
Here are some issues faced by me during single user mode.