How valuable is your data? How would your clients feel if they found out that information about them has been accessed by hackers?
Don't think it could never happen to you, because it can and does!
The first critical point about protecting your data is backups. They provide a way to recover lost data whether from a system failure or accidental deletion. At minimum you should backup each work night and store your backups off-site in case of fire damage or something similar.
Next you need to protect yourself from viruses. These days viruses spread at enormous rates and with out adequate, up-to-date protection you will become infected. This can shut companies down for days while they recover data and get infected systems working again.
Last, but by no means any less important is hacker protection. They are everywhere and are always looking for new vulnerable sites to hack into. Whether they do it just for the thrill of it or if they are targeting you for some reason, they can all do irreparable damage by gaining access to your records and those you keep of your clients.