Efficiency is such a squirrelly parameter, it's really hard to compare one homebrewer's efficiency with another. There are quite a few variables involved: accuracy of volume measurements, did you measure in the kettle before the boil or after the boil in the fermenter? Did you compensate for temperature with your hydrometer? What is the actual potential yeild for the grain you used (you need to get this from the manufacturer)? How old was your grain? Was is stored properly? And on and on. What you are really looking for is a predictable efficiency so that you can dial in recipes and get the gravity and the volume you want every time.
The three factors that I have found that affect the efficiency the most are:
1) Quality of the grind. I have gotten into the habit of milling my grain twice on the same setting. It seems like after the first grind, the kernels are broken, but the actual endosperm is still inside the husk. Even if the kernels are broken, if they are still inside the husk, they won't really give up their starches and your efficiency will suffer. The second milling sheds the husk and allows the broken pieces of endosperm to be fully exposed to the mash liquid. I've tried milling once on a finer setting, but it just doesn't work as well. Try milling twice and see how it works for you.
2) Quality of the malt. I've found the yeild from different brands of grain can vary quite a bit. For base malt, try to stick with one brand where possible for consistency. For what it's worth, I like the Fawcett Bros. malts, especially the Marris Otter Pale for base malt. Get your malt from a reputable source and the get the freshest possible. Store it in a cool dry place and brew often.
3) Sparge speed (assuming you sparge continuously). Although I think this is not quite as important as the first two, this is definitely worth a couple of gravity points depending on how fast you go. For a 5 gallon batch (6+ gallons into the kettle), don't go any faster than about 1 gallon every 5 minutes. Try going really slow the first couple of times, maybe 1 gallon every 8 - 10 minutes, just to see if it makes any improvement. On subsequent batches, speed it up a little and see what difference it makes.
Prosit,