After replacing the speedometer sensor, is there anything else that I need to do before it should start working again? (i.e. reset the ecu)

Thanks in advance.

There's nothing to reset.
Step 1 - get a cordless drill and pull your sensor back out leaving it attached to the harness, turn ignition switch all the way on, do not attempt to start it though, duct tape the end of the drill to the sensor gear, no need to get carried away with the tape either just enough to keep it secured, get someone to watch the speedo (a strategically placed mirror placed on the steering column works too)as you spin it gently, if nothing, reverse drill and try again, if nothing still you either have another bad sensor, bad cluster or broken link between the two. If it does register speed, your ring gear inside the trans is broken or cracked and you will need to pull and disassemble your trans to replace it.
Step 2 - ummm, post back with your results or something lol