1) Position
Is the aggressive villain positionally aware? If he is, then from where did he open? If he opens out of the #1 hole, he's going to be stronger than if he opened from a middle position, the hijack or cutoff. I'd be less likely to play him if he opens early than if he opens late.
2) Player Tendencies
If I don't know much about him, I'll give him a default range, and play presuming a usual opening range. Of course, that can be misleading as even the nittiest player could be on a card heater that makes him seem more aggro than he really is. If I
know him to be a nit, then I'll stay out of his way unless I'm at the top of his range, depending on how nitty.
If I know he's opening very narrow up front, I'll call with any pocket pair, any ( A,x ) or ( K,x ). If I flop a small pair, I'll keep calling as long as an ace or king doesn't roll off. Nits tend to get stubborn when they open with a Big Slick and whiff, as they play so very few
hands; they can always talk themselves into barrelling when they whiff.
I'll usually 3! the nit and expect to take the pot down without a fight. If he's a known aggrotard, I'll call and let him barrel off most of his stack. In that case, you don't want to take him out of the lead.
If the vill has a typical opening range, not too narrow or too wide, I just might 3!, take him out of the lead to set up a play on the flop or turn, depending on how the flop is, and whether it hit what he's likely playing pre. This is a good way to play known FoFs, or "one and done" players who will follow up with a c-bet, but who won't double and triple barrel.
3) Table Image
This applies if they are aware, then it becomes a matter on my table image, and what I think they think about that image. If I've been winning a lot of pots lately, then I can loosen up. If I made a big Hero call recently, especially if they're unaware of the underlying logic/thought process, your more superstitious-minded vills can convince themselves I have some preternatural ability to either read minds and/or know the future.
It also works the other way too. If I've been running card dead, haven't played a hand in several orbits, I might take advantage of my "nitty" image and open from the #1 hole with ATC. I just might steal the blinds with nothing, especially if the other players have been passive and "foldie". It's especially good to bang it with something like ( 7,2-off ) flop ( K, 7, 2 ) and take down a Big Slick on what he thought was a safe flop for TPTK. That'll keep 'em guessing for awhile.
Of course, you can fuggedaboudit if they're playing "group solitaire", not paying any attention. If they're playing with their gizmos, watching that Big Game on the overhead monitors, they probably aren't aware that it's been four orbits since your last hand.
4) Bet Sizing Tells
Do they have any?