The less fluctuation, the better. From what other members have told me, fluctuations of more than 10°F in a 24 hour period can stall the yeast and render them dormant. If you have a basement or your house is on a slab, having contact with that surface would be a good strategy to try and regulate temperature. Otherwise I think Frazier has your best option. Also, ale yeasts operate best between 59°F and 70°F, as a general rule. Of course some work fine at 74°F but most work best a little cooler... Otherwise you're losing attenuation and leaving extra fermentables unused by the yeast.