I'm trying to move a clip on my timeline to play BEFORE the clip that is currently in front of it. When I drag the clip while pressing command, it doesn't slide down the other clip. Instead it just covers up the front end of the clip I'm putting it in front of and I lose the first few seconds of that clip. When I press command, an arrow pops up pointing to the right, as if it is signaling that it is going to push the clip, but that doesn't actually happen.
That's strange, it should work. Be sure to press Ctrl all the time and don't release it until you release the mouse's button.
If it still doesn't work: press ctrl+x to cut the clip that you want to insert, move your current time indicator to where you want to insert your clip, and press Ctrl + Shift + v (paste insert command)