Can't think of too much else. Only these rules:
Turn off anything you don't need...multicasting, upnp, etc.
Make sure the NIC is the only thing plugged into your USB ports. If you have disk drives, mouse, keyboard, memory stick or anything else USB, your bus speed will be horrible. If it's an old laptop, you may have a USB 1.x port which is half the speed of newer USB.
Speed may be computed in "bursts." When you boot the unit, there is a fast burst of LOCAL packets going through and speed looks good. Without constant local packet traffic, readings may be averages (including idle time), which will seem lower. That is nothing to worry about. Your ISP or websites may not be too "swift" either, severly averaging down your readings.