Following these tips will let you sleep soundly at night :- 

1. Mirror the Server’s Disks. This is an absolute must. If you do nothing else, do this. This is the tip that could save you thousands. A disk failure in a server could take 2 – 3 days to recover from and you will need an extremely competent technician to do it, and it still probably won't work properly. A Mirror automatically duplicates the disk so that in the event of a disk failure the system continues to operate as normal.  Mirroring typically only adds a few hundred pounds to the system cost and is now often available as part of the hardware. The very last thing you want to do is restore a server.
    
2. Ensure your Backup software is backing up all of the server. Exchange and SQL Servers often require “agents” which are sometimes overlooked. A missing Agent could prevent recovery of your email system.
    
3. Make sure that your system is fully documented and that you have a documented, tested recovery plan
    
4. Keep at least one set of backup media off site
    
5. Make sure you have an “Emergency Repair Disk” and, for Windows 2000 and 2003, that the Recovery Console is installed.
    
6. Install an UPS. This provides a smoothed power supply to the server, protecting from spikes, dips and power failures which will cause data corruption or loss.
    
7. Apply Service Packs. Microsoft and other suppliers regularly release these Patches which fix many common problems and often address newly discovered security issues. Don’t enable automatic updates on the server which could cause your server to unexpectedly fail. Schedule a time to apply the updates and ensure you have a backup / restore point to recover to if necessary.
    
8. Reboot older servers automatically on a regular basis
    
9. Don’t let the server run out of disk space. Lack of space will cause services to stop unexpectedly, in particular Email, and could cause corruption of critical system files. This could cause days of downtime.
    
10. When planning the size of your disk storage, allow for twice as much space as you think you will need and ensure the backup devices are large enough to accommodate this.

And if you really want to sleep like a log

Have a spare, fully configured, tested broadband router available. No internet access often means no business. A router will probably only cost around £100. How much will it cost to have an office full of people who can't do email? A spare hub or switch is also a good idea. Look for any single point of failure.

Make sure you have documented the system including all the Server & Domain names, Disk set up, Share Names, ISP Usernames and Passwords et al. In fact, document everything you can think of. You’ll need it.

Don't just rely on a complete system backup. Perform separate backups of key applications such as Sage using their built in Backup routines. Perform mailbox backups of Exchange. You can never have too many back ups.

Plan how you could move essential services to another machine or location if the server fails. Pay particular attention to things like the Accounts and Email. How are you going to invoice or communicate with your customers? How long could you survive without these facilities? How much money will you lose if your systems don't work. The posh name for this is Risk Analysis.

The good news is none of the above are expensive options. They just require a bit of time to plan what is required and most importantly to document your existing systems.

As an example, in the event of server failure, it should be possible to relocate Sage data files to another PC in less than an hour and have the Accounts up and running again. At worst you may have to re-key that days transactions.

If you have pre-configured a PC at home, you could even cope with your office burning down just as easily. No additional hardware or software is required for this ; just a plan. It’s not difficult, honest.