You want to make sure that you drop the ghosts behind the mineral line behind the base and have some nice harassment. They can cloak, so this should not be too hard to do. If you see photon cannons, you want to try to finish off these cannons by nuking them, then bringing in the rest of the troops to help finish your opponent off.

Nuking In front or Behind an Army
Maybe you are invading a base or trying to wipe a set off, and he wants to try and pursue your troops, well you can send a nuke in front or behind your army so that you can actually prevent yourself from being wiped out. This will prevent your opponent from pursuing you, so it's a very useful approach that can help you today!