1) Do your homework regarding the car(s) you are interested in BEFORE you walk into the dealership so you don't get 'pressured' into making a choice you may not be comfortable making or get yourself into the position of feeling pressured in general which in turn ruins your car-buying experience.
2) If you have time to 'spring clean' your credit (for example, paying down credit cards so your credit utilization is lower), I would suggest doing so ESPECIALLY if you will need a loan. The better your credit, the better loan deal you can get and since a car loan is for a longish period of time, it's really important to get as good of a deal as you can.
3) Speaking of which, if you need a car loan, do some research on who/where to get the best rates for your car loan (after you've spring cleaned your credit, if you decide to do so).
4) If there is any way for you to both work on paying down your credit card AND putting aside money for the down payment, I would do so. I would not recommend putting a down payment on a credit card unless you either have some superb credit card terms and/or unless you're able to pay that balance off FAST. Generating a crapload of interest for a down payment (if the dealership will allow credit for a down payment in the first place) is not a good idea, in my opinion.
5) Here's another thing to possibly consider - car insurance! If you like all the different cars equally, you may try sharing this possibility of buying another car with your car insurance company and ask if there is a better rate for certain cars. I know in my area, red Honda Civics are priced HIGH for insurance and if you happen to be male, it's priced even higher. (Don't you love it how insurance seems to be the only sector of business where 'discrimination' can happen legally?)
6) If you are not a 'under the hood' sort of mechanic-y type yourself, PLEASE bring a mechanic along with you who you trust to be on your side. A reputed dealer is not a problem, usually, but you never know and a mechanic can sound out potential problems during test drives that the dealer may not (or may) know about.
7) Make sure it's a 'clean' car and not an accidental lemon because of its history.
8) Trust your instincts and gut; if something doesn't seem quite right, then back out.
All that said, that's my advice; maybe other people will have some advice, too.
You've got some good miles on that car; it seems like you've done each other good and it's time for it to retire. In my own experience, once one things goes... everything else seems to want to follow - especially in an older car (10+ years).
Best of luck with your car-buying!