I've made a proposal to a prospect and he suggested we have a 'business lunch' and eventually continue afterwords in their office.
How should I prepare for it? Any DOes and DONTs?
P.S. This is not-off topic as while pitching their products many startuppers may end up in the same situation.
My best advise to you is keep the lunch social and the meeting afterwords business. Don't try to sell or discuss business at lunch unless he brings it up first and then be extremely careful not to be pushy.
The reason for lunch is to get to know you as a person. The reason for the meeting is to discuss your product and doing business.
Great question! This is clearly an opportunity for you to promot yourself and tell more about who you are, why they should invest in you/your ideas, and have a relationship with you in the long run.
Keep it social, show Internet, listen, lough and push your agenda slowly. Don't be aggressive. If they like you, you just earned an extra point in your proposal.