It really determines what kind of relationship you wish to nurture. Are you going to continue to work under the sponsor after the sale?
The classic rule of negotiating is never be the first one to write come out with a number. If you come out with a reasonable first number, you could severely limit your gains. If you try to next level think it, you could get laughed out of the room. Sometimes negotiators write down offers at the same time down on a sheet a paper to resolve a situation in which no one will write down a first offer.
Use next level thinking once you start haggling. If the lowest you are willing to sell it for is 6M, and your initial offer was 10M then cutting reducing your second offer to 8M is too much. Choose something more arbitrary like 9.4M which makes the buyer think they are getting to close to your lowest point.
This also means you should know your lowest point. Another great rule of negotiations is to have a strong alternative. This means explore other avenues for a sale or have projections for where you can take your project in a few years and exit then. If you don't care about the relationship, a tactic to use is to simply lie that you have a competitor's offer. Well since you are meeting tomorrow, make a few phone calls in the morning and see if you can set up a meeting with another potential buyer. If you can convey that you are taking other meetings during the negotiation, it'll strengthen your position.
In the end, feel out the other person and trust your gut. Good luck!