I'd do:

/assist focus
/cast [mod:alt,help][mod:alt,target=targettarget, help][mod:alt,target=player] Power Word:Shield; [help] [target=targettarget, help] [target=player] lesser heal



Edit: But without the silly smiley
If you want to add two modifier keys, so activate a spell when alt AND ctrl are held down then you need to do [mod:alt,mod:ctrl] in the same [] and add mod infront of both keys you want to use.