To do grinds you need alot of speed, to get more speed figure out your own style by using a backwrap.
A grind is where you throw the diabolo into the air, but instead of recatching the diabolo on the string you will catch it on the stick. To do this you want to do a 'soft' catch on the stick. To do that lower the sticdk as the diabolo hits it. The first grind you want to do is a right hand inside grind. To do this point your right stick towards your left and throw the diabolo, catch it on the stick. Make sure to keep the stick pointed up slightly to keep the diabolo from falling off. The do the same thing with yor left hand pointing to your right, this time instead of pointing the stick slightly up you need to point the stick slightly down. With a right hand outside grind the stick has to be pointing down and with a left hand outside grind the stick needs to be pointing up.