I'll post what I've been using for my rogue and berserker to assist my SK.
Under Options (ALT + O)
First, make sure you have 'Q' set to autoattack (or you can replace 'Q' with whatever you use to activate autoattack going forward).
Change the 'Q' (and possibly 'O') to Target Extended Target 1
Now whenever you use your autoattack button 'Q' (or whatever else you may have set to autoattack), it will automatically target the first xtar target. Not always a good thing, unless you make sure to set that to the MA's target.
For group MA you can use the first line off of this hotkey.
For raid MA1 you can use this hotkey.
Note, you can also have a MA2 = /xtar set 1 raidassist2target
or a MA3 = /xtar set 1 raidassist3target
