I'm pretty good at figuring them out, but I'm not always thinking like that. Usually when I think I know who did it, I'm right. The other times I don't really even make a guess.
Even though I was surprised by the ending of Cards on the Table, the person who did it was my first guess. (Only guess, if you put it that way.) The ABC Murders was pretty easy to figure out, because when she makes a murderer look so obvious, it usually isn't them.
The only reason I didn't like the ending of TMoRA (well, I liked it, but not as much as some others) was that the murderer came into my mind as who did it, but I just thought... 'Agatha wouldn't do that'. I've come to learn that she'll do anything.