I wanna get into jamming to songs, most primitive yet effective way this guy taught me a while ago was knowing the key of a song and using scales in the same key. This kinda limits when I want to jam, cause I'm trying to find out the key (physically searching books, scores on the Net etc). So I got bored and got disinterested for a while till now...

Is there a little easier way or formula in jamming? Or do I have to go thru that "spend hours just jamming away experimenting with tons of scales till I develope that beasty instincts" routine like many other players, to get good at it?