When in a power lunch, never be the first to talk business. Do be first to order, it sets the tone and displays confidence. Be willing to turn off your phone. You choose the place but allow them to choose the time. The most productive lunch meetings start at noon in my experience. Choose lunch over dinner. At dinner meetings people often say things they don't mean and have no intention of following through on. You can drink with your buddies. This is business!
Refuse to split the bill, you pay or let them pay. An exception to this is if paid lunches are policy prohibited. Don't leave that lunch without asking for something but not everything, especially if you paid. In that power lunch. Do more listening than talking. Choose a table over a booth. If you want something they have sit next to them at 90 degrees. If they want something from you sit across from them. It shows authority and sets a more serious tone. It is easier to say no from across the table too.
Select a nice venue, not too trendy or pricey. Order your food in a way that suggests you take good care of yourself. During conversation, err on the side of getting their story. If they are interested they will get yours. When you write that short note of thanks, include something from their story. They will be impressed.
In that power lunch: Never be the first one to bring up money. Don't end lunch still talking about money. For every one minute spent on the subject of money spend 5 minutes on content and context of the work or potential work.
Never gossip, ever. Don't name drop unless you have the relationship personally vs relaying someone else's personal relationship. Mirror the other person's behavior subtly. It will put them at ease if done properly/naturally. Never admit to having googled them. Even if they don't admit it being googled feels creepy. LinkedIn is ok. Never source Wikipedia. Just trust my judgment on this one.
Have your business card easily accessible. Nothing more unsightly than watching someone fumbling at the bottom of the purse and pulling at that "last" card with coffee stains. If you are over 40 do not bring a resume. Let them ask for it.
Go in knowing why you are there and remain focused on getting it. Ask good questions but don't pile on questions. Be patient. Show restraint. Don't vacillate in your thinking. Sound interested without behaving excited. Walk out together. Stay in touch for at least one year no matter the outcome of lunch.
Finally, 3 signs it was "just lunch".
1- You hear, "I am not the right person and don't make those decisions but..."
2- You hear, "Send me your information again..."
3- They fail to bring up next steps...before you do
Wear great shoes.