Hey WildMidwest
From my experience, which is not extensive but it seems to work for me, the best time to buy is within the first few months of release or after a year or so.
When a car is first released, the manufacturer/dealer wants to get cars on the road (what better buzz?). If the car is a hit, it will take a year or so for a competitor to match it and the buzz will die down and the prices drop/deals occur. Look at the Ford Focus which is a fine car but has been out a while now and they are offering like $2,000 customer cash. I drove it, liked it, but did not compare to the Mazda and reliability was not there historically from Ford.
Since most new cars hit in the fall and most dealers want to make year end goals, the end of December is a great time to buy. After all who wants the hassle of buying a car when they are focused on Christmas shopping? ...uhhh me
That said deals still can be had...
1)
Know what you want but be flexible where you can
For example, I want a Mazda3 iGT 6MT but I could care less if it is a sedan or hatchback and any color is fine but silver.
The goal here is to find a car that most dealers will have on the lot. By the way, if your goal is a manual transmission, you are already are asking for a uncommon car in an iGT trim (my experience).
2)
Throw a wide net
Reach out to as many dealers as you can. Are you will to drive 200+ miles, if necessary to save $200 or more? Would you purchase from a dealer in another state?
3)
Negotiate through email
Most dealers will want to talk to you on the phone...I usually avoid this. They will try to convince you over the phone and sell you on their dealership but your primary concern right now is price. At least for me, email helps keep it more impersonal till you are ready to choose a dealer.
4)
Request best price with destination
Many people I talk to like to get the out the door price upfront. I tend not to do this because dealers just ask too many questions when you say this. If you are dealing with 12+ dealers at a time. I ask for best price +destination upfront. You want to get down to the top 4/5 dealers and then work on the OTD.
4)
Have a few dealers you can work with and a price that is reasonable?
Check out those dealers through dealrater.com and bbb.org. I realize these sites are not perfect but you get a sense through complaints/reviews how a dealer is perceived.
Now work on OTD pricing....here you really should just have a few items added to the best price +destination. This will usually be title (~$35 - $50), taxes which vary but is fixed for the state you are purchasing from. Ohio is 7.5%...it just went up from 7% and another reason I wanted to buy before the end of year. The last thing is documentation. This tends to vary wildly but $150 - $250 is what I have usually seen in the Midwest. Everything else is add on and should be challenged within reason. No prep cost, no vin etching...etc. Now I would pick my battles, when I bought my last car they charged me $1.25 tire tax....who cares for that price let them have it. Get this price in an email or documented and not over the phone.
Also, would not hurt to get the odometer reading to make sure you are comfortable with the mileage already on the car.
5)
Be prepared to walk away
If you show up and things are not what you anticipated, walk away from the deal you are not obligated to buy. There is always another deal to be had.
I apologize for being so long winded but I hope this helps and is probably common sense but I actually enjoy the negotiation as much as getting the new car.
Best times now would be end of January and maybe February to still buy and look to make a deal at the end of the month. The issue that usually occurs starting in March is that people get their tax refunds and guess what most people do with them? I know dealers know so they are less likely to deal knowing that their are more people with available cash to spend.
All this is really just my opinion and your mileage may vary.
I hope you find the car you are looking for at the price that you want to pay