Experiencing the peace of God inside is a guide.  If you start to do something and you feel like you have no peace about that decision - in other words, you feel really uncomfortable about the idea, and you know it is not fear or lack of confidence making you feel apprehensive - then that is probably not a direction that God wants you to go in. 

A lot of believers call that a "check" in the Spirit.  They decide to do something and then wait to see how their heart feels about it.  If they have peace about it, thenit is a go.  If they don't, then it is a no.