Totally depends on your environment, and many resources you're willing to throw at the problem.
If you have a very large environment, it's almost a requirement that you use some sort of log centralization or aggregation software. That can range from a full-fledged, expensive piece of enterprise-grade software to custom scripts that copy log files to a central "log server" and scan through the for warnings or alerts.
If you have an enterprise-grade monitoring suite, you can usually roll Event Log monitoring into it if desired, though you may not want to. After all, the monitoring system will alert you to problems, so adding all your Event Logs to it could start to create a case of information overload.
Or, if you're in a smaller environment (as it sounds like you are), there may not be a need for anything beyond what you can find natively in Windows.
I was a one-man IT department at a shop with only about a dozen Windows servers a while back, and no budget for software, of course, so my solution to Event Log monitoring was a simple script that opened the Event Log Viewer, connected to all the remote server Event Logs, and applied a filter to only show me warnings and errors. I ran that first thing every morning, and it became part of the daily checklist of things to do to keep the environment limping along for one more day.