It's interesting looking at the list. My first reaction to the list is to take it and separate everything into two categories of priorities: personal and impersonal.
Falling in love with someone: I gauge my feelings for them. How do they make me feel? How do they enrich my life? Am I becoming too dependent on them? After that, I look at their age, where they are in life, their viewpoint on their own life. It's interesting how all 3 of the people who viewed this as a choice are TJs. :P
Choosing a pet - What kind of pet would be the most exciting to have? Which one would fulfill me more? After those two questions are answered, I look at which pets I can realistically take care of in my house.
Choosing a career - This one is kind of easy but kind of complicated. I'd just find something that I could relate to and understand, but will still be needed when I'm able to do it. I'd look at the requirements on the job. What do people do in the job exactly? Can I go talk to people that have that job for firsthand experience?
Buying a car - I would do a lot of research beforehand. I would want to know the things I should be weary of when buying a car in the car itself or the financing. I would look at the car's longevity and maintenance requirements.
Grocery shopping - I plan out my meals over the next week or so. I map out calorie usage, money spent, and look at the things more efficient for calories vs. cost. Then I start taking that list and find things that are personally appealing.
Buying a pair of shoes - What kinds of shoes do I already have? Do I have any shoes similar to the one I want? Is it close enough to warrant not buying it? For example, I chose not to buy a pair of shoes I wanted even though I had the money just because it was a different color of a pair I already had.