Can anyone help with some advice on splitting a colony?

I am new at bee keeping, and currently have only one colony, which at present is housed in two brood boxes. Today’s inspection showed that the bottom box has 8 out of 10 frames, with both sealed brood and larva, where the top box has 4 or 5 frames of capped brood, and another 2 frames of eggs.

The queen was in the top box today, and in bottom box last Saturday, so she is busy and readily moving between the two. Haven’t seen any queen cells yet, but did notice a queen cup on one frame in the bottom box.

What I would like to know is, when would it be a good time to try a split or artificial swarm, to increase my stock? And any hints and tips on how to go about it?