Dear Paul, 

Here are some quick pointers on your two questions:

The conditions required for doing a good vocational discernment? I think the fundamental condition is to be honest, really and truly open and willing to follow Gods will, and free from excessive attachment to anything that is not God. In my experience the whole question of vocation hinges on this disposition. If we dont have it, or if it is still weak and tentative, we face lots of obstacles, insecurity and unhappiness as we go about trying to discern and most importantly, trying to follow Gods plan for our lives. This disposition is so fundamental it affects not only our acceptance of the signs that lead to discernment, but also our ability to act on what we have discerned and actually take up the vocation, and it affects also our fidelity our whole life long, as we follow the path we set once out on.  

The second disposition is related to the first. We should be honest and open in our dealings with our spiritual director and vocation director. Only then will they be able to counsel and guide us prudently.

The signs that the answers we get are reliable as regards a calling to certain religious life? I hope Im interpreting your question properly. The answer regarding our vocation, the answer to the question if we have one or not, is not like the conclusion to a mathematical problem its never as clear or incontestable. It is something like asking a husband-to-be to prove he is not making a mistake. He can be satisfied, convinced, sure that what he is about to do is the right thing, but he cant prove it. So, if you have a spiritual director or if you have spoken in depth, openly, honestly, not hiding anything about yourself, to the vocations director for the religious order you are interested in, and if you have prayed and asked for light and help from God, and if all the usual conditions are in place, you can be pretty sure you are making the right decision.

What are these usual conditions?  The necessary physical health, psychological maturity corresponding to your age, sufficient intelligence for the studies, a personal attraction to that way of life for spiritual reasons, the ability to live in community, willingness to give yourself totally.

God bless, and be sure of my prayers.