One easy way: Macro.

This command will make you cast Cure on the target which your mouse is *pointing-at*, no need to even select the target:
/ac "Cure" <mo>

For completeness-sake, you need to create a macro like this:
/micon "Cure"
/ac "Cure" <mo>
/ac "Cure" <target>

Means:
Your macro icon is "Cure".
Try to cast "Cure" at the mouse-over target.
Try to cast "Cure" on the selected target.

You can also add:
/ac "Cure" <me>
But for some reason, I don't like doing this, and just use F1 to select myself always.

Hope this help.

Oh and btw, there's a "Target Filtering" setting, and the default key to trigger it, is X.
Hold down X, and you can only select those targets which is the type selected in "Target Filtering" setting.
Try it out.