I'm with Grumpy Mike on the extra flux being extraneous, but it probably wouldn't hurt as long as it doesn't get into anything. But it might help more if you have a mediocre soldering iron.
Really the two biggest things is to minimize contact to the motor. While it is designed to be soldered to, it also has limits (which it probably says in a datasheet somewhere that may be inaccessible). That being said, you do want a good solder joint, which the easiest way is to tin both the wire and the motor, then solder the two together so they are all in one continous piece of solder. It should be shiny, and cover both parts (Though with the motor tab, the part is basically one side of the tab.) I would also recommend using heat shrink to cover the joint to reinforce it, and also figure out a way to strain relieve your wires as close to the motor as possible, as that joint will eventually break if left unattended, since motors tend to vibrate. Basically, you want there to be no force being applied to the joint in any direction, or it may just break off after being used for a while.