I ride 26 miles roundtrip each day to my carpool's house.

Just for some background info, I live about 1 mile up on a hill. Once I get down that hill, it's a slight uphill until I get there. Reverse that procedure in the evening.

I really would like some advice on how I can effectively use this time as training. Should I be doing intervals, or just trying to maintain a higher speed throughout?

Thanks in advance for all the advice!