Yeah, dave Miller's books are ancient comparatively speaking. Had them and Papzians books and they were great ... back in the early 90's.
As far as temp control goes, if your ambient is 68 that is far too high for most ales and, as was stated, you need to monitor beer fermentation temp - which can be 4-6+ degrees over ambient. A swamp cooler, as was described, works well. But nothing beats accurate control with a fridge/freezer and external thermostat such as a Johnson or Ranco.
Fermentation, and that includes Temp Control and Pitching enough yeast, is the single most important process of brewing. Even if all your other processes are sound, if you don't have good fermentation techniques your beer will never be as good as it could be.
And that is why I say it should be your next step.