Keep them warm
Most house plants need a temperature of 12-18⁰C. They dislike large temperature fluctuations, so position them away from cold draughts and open windows or doors. If they're on a windowsill, leave the curtains open if you can, as they trap cold air at night. Alternatively, move plants off the windowsill at night. Also keep plants away from heat sources such as radiators and fireplaces, which can scorch delicate foliage.