Like buying a car? I went through this last January so I still remember most of it-
Very logical progression, using prior experience with specifying technical design/etc. like I do at work.
1. What are my needs?
1a. All-wheel-drive for accelerative traction
1b. Roomy enough to hold my fat-ass
1c. Roomy enough to hold my friends
1d. Price brand new <$24K
2. Prioritize those needs
2a. Price brand new <$24K
2b. Roomy enough to hold my fat ass
2d. Roomy enough to hold my friends
3a. Prior experience tells me Japanese vehicles usually have great track records.
4a. Subaru. Cheap AWD, Japanese, and a buddy of mine swears by him (well, his parents do, but him by extension). Here I'm diverging from logic a tad and going by word-of-mouth alone.
5. Line up financing and find the best deal
5a. Line up financing. I shuffled money around and applied for one of those "blank check" type of online auto financing things.
5b. Locate local dealerships. I used edmunds.com to field a bunch of request-for-quotes for all the nearby Subaru dealerships.
5c. Test drive different Subaru models, evaluate specific features and perform non-linear shoot-from-the-hip logic. This is where everything turns blurry and I logically evaluate the different featuresets--presence of limited-slip differential, hill holder features, rough "feel" for the acceleration (determined by test driving), feel of the vehicle's handling (determined by test driving), etc.
6. Select ideal model and narrow the search.
6a. Subaru Forester has the ideal set of features and at the right price. Found a dealership in Leesport, PA that was practically throwing a brand new one at me (knocked the price down a lot without me even asking; the dude was extremely straightforward with everything, no bullshit, honestly I think I was dealing with an INTJ or maybe ISTJ there [based on other factors I observed during the purchasing process]... he was cool.)
7. Execute the purchase
7a. Arranged the time to test drive & purchase, dressed nicely, put together a binder with damned near everything I could possibly ever need with me--full breakout of all Subaru models & full specifications, price quotes from all the local dealerships, a full copy of my credit report, printout of all available incentives, map to all the local dealerships (in case this one didn't pan out I'd know how to get to the next one), title information for my current car, kelley blue book printout for my current car, etc.