What would be a propper way to back up a huge db while server is up

Hi there, how would a backup procedure look like on a mysql server with root access to make a backup while the db is up and running. As fast as possible The db is more than 100 MB. Would this be: - lock all tables writing (how would I do this on the whole db containing lots of tables?) - flusch the tables (the whole db? How?) - copy the dirs with the dbs - unlock the db (how?) Thanx for any help, Andy