There are 3 aspects to the negotiation
1. the intrinsic value of your proposition
Here due diligence is undertaken namely upon the idea, market, team and product as well as if any IP can be protected and what traction has been obtained to date.
This is what most people speak about when they talk about valuation, but it does not stop here.
2. Market heat.
Try raising money for a crypto startup now, not many are interested other than enthusiasts. But in late 2018, you were the hottest prospect. So timing is key.
However, my personal stance, is that you should not prepare for market heat. Build in what you are uniquely and comparable advantaged to build.
3. Cash runway.
A startup without cash prepare has time to feel the market, enter into parallel discussions with various investors and may even as a result get multiple offers.
A startup with a limited cash runway? with a few months left, that becomes a buyer's market, where investors have the upper hand.
Basically any startup as of the Covid19 pandemic, has little negotiation power (other than a few exceptions who are winning from the moment).
My experience on this topic is to ensure as a founder you know what you need in terms of ask, and what you want to build and by when. As long as you do not give up to much, you should be willing to compromise on valuation, as long as the other party will be a good partner in terms of providing cash today, creating network and business opportunities and be willing to support future equity rounds, either through investment or at least as an ambassador.