30-50lbs is a typical jump. Normally when you think about it you're really splitting that in half by two legs so it's not THAT big of a deal. It's just getting your CNS and system used to suppoting that extra weight, once you get out of your own way and get your head right, you should be able to make that kinda jump and handle it for 4-6 reps no problem. It's up to you though..if you're comfortable wiht smaller jumps then it's best to stick with that kinda increment increase.
funny, everyone else says 5-10lbs, but I agree with wicked, only on legs, I like to make big jumps on legs, it is extremely intense and difficult, but it makes you feel good at the end of the day knowing you accomplished something.
5-10lbs on a leg exercise, to me, just doesn't seem like enough to make a difference