I'm not a true race walker but just finish my first walking half marathon. What has helped me go faster is starting to do some speedwork. Ohmom mentioned doing intervals. And I used interval training 1 day a week during the last several weeks of my marathon training. After warming up, I would walk 3 minutes then either walk fast or slow run for 1 minute (I'm hoping to transition to a walk/run Galloway type method). Then repeat for a total of 8 times before cooldown.
A less structured type of speedword is fartleks. While there are now routines called fartleks, originally it was impromptu speed up "race you to the tree" type of speed work just like when you were a kid. For example The trail I worked on had 1 section that was marking with 40yd, 100m, 200m and 400m lines. One day I decided to try a 100m dash just to see how fast I could run. I finished it in 29 sec or about a 7 min/mile pace faster then I ever dreamed possible. I was huffing and puffing at the end and could't have kept up the pace any further. After that, I went back to my 17 min mile pace for the rest of my walk.
Those things cut my long distance walking pace form about a 17:00 min mile to a 15:40 average for my half marathon and my final .2 mile at a 13:20 pace.
One final thing, you don't want to do this every workout. Probably no more than once a week. Monday's I did speedwork, Wednesdays I tried to focus on consistancy, and Fridays were Long Distances work.
Good Luck and you will probably get faster over time even with any speedwork but for me it provided variety to my workouts and made the improvement happen more quickly (or at least it felt that way).
