Here are the most important things I’ve heard throughout my discernment thus far, in roughly descending order of importance:
1: Yes, you could indeed have a vocation - explore it further. (As opposed to: you’re too young to be thinking about that. You can’t know your own mind yet.)
2: The Sisters like young people and want to help you in any way they can. (As opposed to: brace yourself for an uphill battle of constant scrutiny before they’ll let you through the door.)
3: No, your student debt is not going to ruin your life. (As opposed to: it will take you five, maybe six years to get rid of it, and hopefully by that stage you will have a good job and a boyfriend and moved on from this idea about being a nun.)
4: No, this allergy/knee injury/blot on your medical record isn’t the end of the world. *(As opposed to: it’d be a liability, so perhaps find something else to do.) *This sounds like a silly one, but I sent in a general information form to the Nashville Dominicans a few days ago, and was practically hyperventilating when I realised that I had to mention two mild medical issues in two consecutive answers: I was convinced that the next letter I’d get would be a polite apology for being unable to consider me as a future vocation. Was that what happened? Nope! (Not yet, anyway!)
5: The religious life isn’t blissful all the time, but neither is any path in life. Some of the difficult parts are… so be prepared to encounter them, but remember, you can overcome them because you’re doing this for Christ. (As opposed to: you’ll have to do fasting and penances, you’ll be getting up before dawn, you’ll be caged up with people you don’t like, and you’ll get time off Purgatory if you take it in silence.)
As you can probably guess from the tone of the above, a fair bit of what I’ve heard in my discernment has been negative, and it makes the words of encouragement really really precious. I actually went through a stage of severe anxiety about my vocation earlier this year, when the negative advice seemed to be coming from all sides. What set me back on track at that time was a beautiful book called “What Must I Do?” by Sister Mary Paul Reilly, written in the early 1950s, which said not to worry inordinately about those sorts of issues: “Christ is courting the object of His desire, and He makes His intentions known by arousing in her an ever-increasing response to His love” (pg 8).
Upon reading that sentence, the fear that had been building up as the result of too many warnings and checks upon my enthusiasm evaporated: I remembered that because God loved me and wanted me, all manner of things would be well, and that was the equilibrium I desperately needed. So in answer to your question overall, I’d say that any advice set in the positive frame of love for God is good, and a single encouraging sentence is priceless.