It depends largely on what kind of cigar you're using, but general tips:

-Be sure to get the leaf (or both leaves if applicable) very moist; dry leaves tend to break very easily.

-Remove any stems from the ground bud. Sometimes, a tiny bit of stem that was attached to a bud will come out of the grinder sharp. These little things love to tear your paper/leaf.

-If it's too skinny, add more pot! There's no other (good) way to make a blunt fatter, except perhaps making it shorter.

When are you tearing them? I could give you specific pointers about splitting the leaf, rolling the inner leaf, or whatever else is giving you trouble.