There seems to be a whole field of study on new car buying techniques and different people will swear by different approaches and others who will swear they don't work.
If you are waiting until next summer, hopefully things will be back to a more normal situation...because right now, things are crazy with the chip shortages.
Assuming you aren't set on a particular brand, look up what rebates are available from each brand. If nothing else, you can use that as a negotiating point if you want an extra grand or two off a brand that doesn't have a rebate.
Used to be you could look up the invoice price to give you a starting point (haven't bought new in a long time as it doesn't make financial sense, so not sure if it's still easy to pull up). Keep in mind, the invoice price ignores what is usually a 3% kickback to the dealer, so it is possible to get it at invoice price and the dealer still makes some money. You aren't stealing the food out of the salesman's kids mouths...if your offer is too low, they won't sell.
Assuming you live in a reasonably populated area, I wouldn't worry about being taken seriously. If they don't like your offer they will counter. The biggest thing you can do is if you don't like their counter offer, is walk away. They will try to play head games with you and they most likely will chase you out the door if you get up and walk away. Be prepared to walk away if you don't get the deal you want. If you are in a reasonably populated area, worst case, you go 10 miles over to the next town and talk to that dealer with a much better understanding of what the first one was willing to accept.