(American English simplifies the whole affair by plumping for 'licenses' and 'licensing'.)
Some of our writers were having trouble remembering the spellings of the two words – so, bearing in mind that 'licences' is a concrete noun while 'licensing' is an abstract noun, I came up with a mnemonic for them:
If it's something you can see, then you spell it with a 'c'.
Of course, while this works with 'licences' and 'licensing', it doesn't apply to other things that our writers might see around them, such as calami candwiches. Still, one step at a time.