I don't know what your wiring package looks like but consider that a relay normally has 4 parts:
1) Input power - this is the power that it receives and is available to send to a controlled device
2) Output power - this is the power going out from the relay to the actual device being controlled
3) Signal/relay coil Input - this is a 12v wire coming in that will power the coil to close the power contacts
4) Signal/relay coil ground - this is the ground for the coil that is used to close the contacts
In your case, you need to supply the relay with input power (#1) above. Due to the inrush current of electric fans, I would think that you run a wire from your Ign source to the circuit breaker and then to the relay power input. The power output wire (#2) is then sent to the fans to power them up. This output wire is actually protected by the circuit breaker so I don't see a need for an additional fuse. But if you want, you could put the 30A fuse in this output wire.
For the relay coil, run a wire from an Ign source through a smaller fuse (maybe a 10A) to the relay "Signal" input (#3). This wire will really only run less than 0.5A so an 18Ga wire is appropriate. The ground for the relay coil is actually supposed to be the coolant sensor which will ground once the setpoint temp is reached. But since you want to run the fans straight on when the Ign is on, just run this wire to a good ground (#4).
Turning the fans on with Ign means they will run on high anytime the key is On including when the engine is cold or even cranking the car. Not sure you really want that but up to you. I'd suggest running the relay coil power (signal input #3) through a toggle switch so you can flip them on once the engine is warm or after started anyway. But you can't forget or you risk an overheat unless you have a warning light/gauge to tell you to turn them on!!
Alternatively, you could instead run the relay coil ground (#4) through the toggle switch without any fuse protection (since your #3 wire would already have a fuse). Then, if this wire ever shorts to ground, it only turns the fans to On. But either way, if you use a toggle switch, you have to remember to turn the fans on.
