I'm new to the Multiplayer Rodeo here so please bear with me...

I am just getting started and I'm trying to figure out how to deal with movement. I've looked at the question Best way to implement mouse-based movement in MMOG which gives me a pretty good idea, but I'm still struggling with what kind of data should be sent to the server.

If a player is on position [x:0, y:0] and I click with the mouse on [x:40, y:40] to start movement, what information should I send to the server? Should I calculate the position based on velocity on client side and just send the expected location? Or should I send current location and velocity and direction? When the server is updating the clients on the players' whereabouts, should the position be sent only, and the clients expected to interpolate/predict movement, or can the direction sent from the client (instead of just coordinates) be used.

My concern(or confusion) is regarding the ping/lag frequency of data update and use of a predictive algorithm, as I'd like the movement to be smooth even with a high latency, and prevent ability to cheat(though that's not the top priority).