If you want to use the AVA skill to run/move faster activated AUTOMATICALLY as you press the keybinding to mount:
It is not possible to automatically execute skills. You need to manually do it.
What would be possible, I guess, is to switch the action bars (weapon sets) to number 1 or 2 if you mount the horse.
But you won't be able to execute the skill then anymore without getting unmounted again
Or does this AVA skill not unmount you if you use it sitinng on your mount? (I really don't know)
The easiest way would be to just execute the skill manually and THEN mount afterwards.
There is an addon which shows you the currently active weapon set/action bar by help of a number 1 or 2 (you can change the font, size and color by chat commands. See the addons description):
http://www.esoui.com/downloads/info7...aponbarId.html
Or you can use TweakIt from circonian to show the current weapons as small icons:
http://www.esoui.com/downloads/info9...nsTweakIt.html