Now you're delving very much into a black art
The short answer is there really is no easy way, especially if they're actually
good at mixing up their play. Patterns or glimpses of reads should still start to emerge over time (for example, very general reads like this person is only playing TAG style hands, or they're playing a loose style), but in the first instance you probably just need to concentrate on playing solid poker yourself - scale back the buffing and subtle moves and just play things by the books until you get a better handle on the player.
There's another option too, of course, and it's probably the easier one - unless you're playing heads up, there should be a bunch of other players at the table. So just avoid the player you can't read, and focus on taking chips from the other players instead. You don't always have to beat every player at the table - you just need to be able to take money off a few of them.