Depending on your choice of backup software, you will have several types of backup paradigms at your disposal:

As an example:

You would do a full backup every Sunday morning. Then, from Monday to Friday you would do an incremental backup.

This would mean that if you wanted to do a restore of Thursday's data, you would have to have to restore from the following backups:

That could easily be 5 tapes, which you have to shuffle in order to restore something, which you may find to be too time consuming for your needs.

Your other alternative is then:

Do the full backup on Sunday morning, and then do a differential backup each day after that.

Then to do a restore of Thursday's data you would only require:

Obviously, keeping differential backups requires more storage space on your backup media, so you'll need to decide which method works best for your situation.

Some backup utilities allow for an even finer grained set of levels (0-9), where each level only does a backup of the data that's changed since the last backup of the next lowest level.

In other words; level 0 is a full backup, while continually doing a level 1 backup after that would be the equivalent of a differential backup.

Doing a backup at level 0, 1, 2, 3, 4 and 5 would be the same as doing an initial full backup, and then following that by incremental backups through the week.