5. Start 'er up and pop the hood
When you start the vehicle, always check the air conditioning and the heat. If it takes more than 15 seconds for either one to work, make a note of it, since those repairs can be expensive and complicated.
Then walk out and open the hood. You're not a professional mechanic, but you can take note of what I call the big three: fluid levels, leaks, and sounds. When the vehicle is running, look at the coolant level, any oil build-up around the engine, and the transmission fluid dipstick which should measure "cold" on the lower divot on most vehicles. Listen for any ticking, rattling, or other abnormal noises. Not comfortable doing all that? An experienced mechanic who has looked at thousands of vehicles can lend you their eyes and ears later on.