I used to have nightmares about overhead, but I have become pretty good at it.
First is you have to recognize them first. In certain situation, your opponent gives you tips that he's going to lob. In other situation, it's just obvious that he's going to lob..
If it's just a technical problem, you just have to practice. One thing that particularly help my overhead is hitting it against wall. Well, more like you smash it into ground, and it will bounch up against the wall.. Start out easy, and increase pace, see how many you can do w/o missing..
Another thing is, "lift". The stronger your core body is, the better coordinated you become with your arm and leg. At least I feel like that way. Do some ab work, and bench press...