Also another way is to accent certain beats, or have the measure divided up into groups.
Play these on your thighs, every one, or accented beat, should be played either louder or with your dominat hand and the other being 234567... and so on.
In 7/8
12 12 123 <- I like this one the best
123 12 12
12 123 12 <- sounds weird.
12 12 12 1 <- this one is cool
1 12 12 12 <- same thing backwards
123 1234
1234 123
123 123 1
1 123 123
make up your own now
in 11/8, I like this one because of how many options there are.
1234 123 12 12
123 123 123 12
12 123 12 123 1
1234 1234 123
there are tons more, I didn't make too many so you can make your own.
Then try insane time sigs!
23/8
1234 123 123 12 123 1234 1234
1 12 123 1234 12 123 1234 1234
these are hard to groove
Then, using the same method as before, 'delete' beats to form cool rhythms!
These ideas are the tip of the mathcore/syncopation/polyrhythm iceberg. make up stuff, branch off from ideas, through everything out play as if a monkey was playing, try to make computer noises like the old dial up sounds. Record sounds you hear while out in the city, like jackhammers, car horns, people talking, birds chirping, leaves rustling, babies crying, someone screaming. Then go home and work the rhythms/notes out on your instrument, or while chillin on the bus try tapping it out on your thighs or the seat.