In 1915 Kazimir Malevic, quite a famous abstract artist, painted a true "masterpiece", lol.
It was called "Black Square", and for good reason, because it was, err, a black square, that was it, a jet black square, in the name of abstract art, and it probably sold for millions and had art critics drooling over what this mysterious black square represented. Look it up if you doubt me.
Now I'm not saying for one minute it was a good piece, because it was rubbish imo. But it was abstract art. That's why I said there's no real skill involved other than a good imagination, not in Malevics' case though, lol.
As I already mentioned, I think a decent grasp of colour theory helps more than anything, because having the colours in the right place to compliment each other is immensely difficult. It can make or break a piece of abstract art. I'm not a trained artist by any stretch, I wish I was, because the first thing they teach you is colour theory and I'd find abstract art a lot easier if I had been trained.