While ubered, don't stay staring into their uber, you have to find killable people to force their medic to divide the uber or to get picks. (there are cases you can do the staring while blocking their passage, like when defending badlands last, so they don't get close to the rest of your team and waste their uber)
Also, in a uber vs uber situation, the lesser teammates you have near the uber, the better (this is not the case when you have a full uber advantage).
If all you can see in a uber vs uber is the other team's ubered combo, you have to think about getting a positional advantage for the after-uber fight before the uber is over.
And don't care too much for the initial damage, this won't matter too much in the after-uber fight because your hp will get healed during the uber.