A full backup
Just like any other file on the network, the key to a successful database recovery is to have a full, current backup of the MDB and MDF files. You should be taking incremental copies of the database files at least once a day, combined with a full backup at least once a week.
A log file backup
A 100% accurate database restore is reliant on having a completely up-to-date set of log files that corresponds with data access and update operations. For industries that are heavily regulated, like finance and banking, the log files are essential to prove compliance.
Microsoft is keen to point out that you must have “enough” log backups available for a restore sequence, including the tail-log backup, before beginning the process.
Sufficient spare disk capacity
In order to test the restored data is correct, you will need to restore the database elsewhere first. This will then give you a chance to test the restored data and ensure that there is no corruption, and that you have an up-to-date set of records that gives a true indication of state before the crash/deletion/corruption.