Dont be hard on yourself. Some of us out here dream about an average speed of 15 mph. I did 40 miles the other day and it was pretty flat and my average speed was 13.5 mph. So Im not fast, so I may never be able to join some clubs because Im too slow but I love to ride and Im out there giving it my best and thats what really counts.
So keep riding and giving it your best and remember some days just suck.
The most effective way to do it, is to do it.
Amelia Earhart
2005 Trek 5000 road/Avocet 02 40W
2006 Colnago C50 road/SSM Atola
2005 SC Juliana SL mtb/WTB Laser V