I'm just moving all my websites over to a basic 512MB RAM/1 procsesor droplet for the first time, learning how to make virtual servers and getting all the databases in with proper security and such. I've moved over 3 or 4 of about 15. According to Webmin, I'm already utilizing on average about 40% real memory / 3% virtual memory, but typically not much processor utilization. None of these sites do I expect to hit random massive bursts of traffic either.

But for a person who knows basically nothing about being a sysadmin, when do I know I need to upgrade? I don't want to start crashing before I find out.