Mix up but not too stiff or you'll have a job to get an even coat.. Trowel a 3-4inch band of material onto the joint. Bed the tape in the joint and then run your trowel or knife along the paper, forcing out any excess material. Don't press too hard or you'll not leave enough material for the tape to bond to. Lightly coat the tape up to fill out the tapered edges of the boards. Leave to set. Easifill sets in 90 mins approx so can be taped over again quickly. For the 2nd coat, remove any nibs and run another coat of material along the joint , finishing it approx 10 inches wide. Because you have used paper tape, it is unlikely that 2 coats will be sufficient, so apply a 3rd coat once the second is set, finishing at 12-14 inches. If you were to use scrim, you can do it in 2 coats with Easifill as it is really a 2 coat system. Just remember that the more coats you apply in quick succession, the longer it will take to dry, ready for sanding.
I bought a curved trowel once, waste of money.