How should I stop condensation on my roof that's leaking into my home?
The two main reasons I know of for condensation in an attic are a lack of air circulation from soffit to ridge vent and air leakage from the house typically due to an improperly vented exhaust fan or insufficient vapor barrier between the insulation and top of the ceiling.

I'd focus on the first cause by making sure your soffits are vented and there's a clear path from the soffit up to the ridge vent. Too often dirt and debris block the vents and homeowners force insulation all the way to the roof blocking the air flow. After that is checked, follow the ducts from any bathroom exhaust fans to make sure they vent outside the home. In a best case, they go out the side of the house, well away from the soffit vents, or at least out the roof. But at a minimum they should go out near the soffit (where much of it will get sucked back into the attic) and not left venting into the attic directly. Lastly, check under the insulation to be sure there's either the paper facing of the insulation or a plastic vapor barrier between the insulation and the ceiling below.