8. Defragment your hard drive
One of the long-standing maintenance tasks for computers has always included defragmenting the hard drive. Fragmentation occurs when individual bits of data that make up a file are stored in scattered sectors across the physical platters in a hard drive rather than being stored in sequential sectors. When this happens, the hard drive takes longer to locate and access those files, which can result in significantly decreased performance.
Defragmenting a hard drive improves performance by placing all the bits that make up a file next to each other on the physical drive. Optimizing a hard drive (a phrase typically used interchangeably with defragmenting) organizes similar types of data (such as system files, applications and user documents) sequentially. This can result in increased start-up and application launch times, but most utilities will perform both defragmentation and optimization at once.
Some file systems are much more prone to hard drive fragmentation than others. The Windows FAT system that was introduced in the '80s (and later superseded by FAT32 and then NTFS) was probably the worst offender in terms of fragmentation.
The current Mac OS X Extended file system (and its variations) and Leopard itself do not produce nearly so much fragmentation. In fact, since the release of Mac OS X Panther, Macs rarely divide up the bits that make up a file. If a file is modified and saved, the entire new version of the file will be written as a whole in a series of continuous sectors.
As a result, unless a Mac's hard drive is particularly full and you are working with very large files (such as digital video), you probably don't need to worry about fragmentation. However, defragmenting can improve performance somewhat, and most third-party utilities that defragment or optimize a hard drive will also verify and repair the directory structures as part of the process. (Mac OS X doesn't come with such a utility.)
9. Allow Apple's maintenance scripts to run
Mac OS X includes a series of three maintenance scripts designed to run daily (every night at 3:15 a.m.), weekly (every Saturday at 4:30 a.m.) and monthly (the first of every month at 5:30 a.m.). These scripts perform common maintenance tasks for several of the Unix underpinnings of Mac OS X. While most users won't see any overt problems if these scripts aren't run regularly, they do perform some important functions, mostly related to conserving disk space.