Compost Tumbler - Am I doing it right?

Hi

I've made a compost tumbler out of a recycled large blue barrel. 

Started filling it with all sorts of stuff...leaves...cow poo...kitchen waste...peelings etc.

How do you know if you have the correct mix of carbon to nitrogen waste?  Is there a way of knowing just by looking at it that it needs a bit more of one or the other?  I think mine might be light on carbon but without experience of this it seems hard to tell.

Many thanks for any replies.

Adri

Found this for you - hope it helps.
http://www.planetnatural.com/tumbling-composter/