Facing change/transition is a perfect time to use our "scrupulously honest" observation skills. I've found that assessing how ready we are for a change is greatly helped by accepting our true feelings (all of them, of course).
After agreeing with ourselves that will look at a situation clearly and openly (scrupulously honestly), we can move through some steps that guide us toward a final decision about how to proceed.
First, we should predict we will encounter an assortment of feelings regarding the situation. Rarely in life do we have only one emotion at one time; life is far more complicated than that, and human beings are far more complicated than that. Anticipating we'll have more than one feeling (or more than one "shade" of feeling) about what we are facing helps us not feel blindsided by our experience (it also helps remind us that we aren't nuts for possessing a range of emotions- we are quite normal).
Second, we should accept that we may have ambivalence, even if on balance we are in favor of the change. Because, again, life is complicated and multi-faceted (that's why the word "bittersweet" was invented I think). Ambivalence, in and of itself, doesn't mean we are making a mistake.
Third, I find it useful to pretend I'm a lawyer or scientist, and then try to make a case for both sides of my decision. Say I'm thinking of making a major living situation change, as is MysteriousDream. I'd try to come up with all the arguments I can think of for why making the change is the best decision and why it is not the best decision.
Notice I didn't mention the phrase "right" or "wrong" decision. To use these words often gets us into that perfectionistic thinking stuff, which is never helpful. In general, I prefer "best" decision, because that word implies there may be a variety of options possible, and that several or many of them have merit. The goal is ultimately to choose the option with the most to recommend it.
It's also worth remembering that sometimes we're choosing between a bunch of terrific options, all of which we are interested in and any of which we'd be satisfied with. Other times we must choose between options, none of which are appealing- or worse- and the chore in these times is to choose "the most tolerable" or "the least awful" option.
Finally, I try to tell myself that the decision I'm making is based on my most thoughtful and educated decision-making skills, and the most thorough information I have available to me at this tim e. I can't predict the future. All I can do is make the best choice I can in the present. Most decisions (not all, but many) can be amended (some can even be reversed) down the line. In fact, I like to think of life as a big experiment, in which we make decisions, see what the effects are, and then make modifications based on what we've learned. This way of thinking helps take some pressure off- we don't feel so much as if we have to make "the perfect" choice (the idea of which we all know is a myth, especially for the bigger decisions in life- we might be able to choose "the perfect pair of shoes" but that's not the kind of decisions I'm talking about here).