A generational backup system is the best. Have tapes marked Monday, Tuesday, etc. and use them accordingly. Then save those tapes for three or four weeks before you reuse them. If you don't want such an elaborate system, at least alternate the tapes every other day. That way if you discover that the drive can't read yesterday's backup, at least there is a tape from the day before.
Tape is cheap.
Use a lot of it. Nights and weekends are the best time to do backup. Sending all the files that were changed that day will bog down the network. A more important reason is that open files can't be backed up. Some software packages will simply skip the open files, inviting a catastrophe.