I agree with Camille about clear pots. If the roots are dry they look Silver, if they are still green don't water.
If you don't have a clear pot another tip is to use a wooden spike which you insert into the medium right to the bottom (carefuly not to damage the roots). Leave it for a couple of hours an then remove it. If it is damp then you don't want to water yet. If it is dry then it needs more water.
I use the wooden spike used to support a flower spike. I leave it in all the time and just pull it out to take a look. I alway use the same hole in the medium so I know it's path through the medium is clear.
I also agree with Camille on
how to water. You either want to soak or run water through, in both cases drain thoroughly afterwards.
As everyone has said how often depends on lots of things and if your bark is new or you are in very dry conditions then you will need to water more often than a more humid enviroment and/or older bark.
