Both United Future leader Peter Dunne and Act MP David Seymour are angling for ministerial positions in a new government.
On Saturday night's vote, National has enough seats to govern alone but Mr Key is reaching out to the parties which have supported his government for the past six years in an effort to shore up a more comfortable margin in the House.
Mr Key is also aiming to avoid "third-term arrogance".
Mr Dunne and Mr Key met this afternoon in a meeting Mr Dunne described as warm and friendly.
"We've had one meeting today which has lasted about an hour. I've never been in any negotiations that have been wrapped up that quickly. I don't think this will take too long."
However, he acknowledged he was in a weaker negotiating position than in the past.
"Look, I'm not going into the detail of what might be in an agreement," he said.
"This is a slightly different situation in that we're dealing with a majority government this time as opposed to one that was a minority on the previous occasions.
"But we've just really had a general scoping talk today and there will be more talks over the next few days."
Mr Key is expected to meet Maori Party co-leader Te Ururoa Flavell and new ACT MP David Seymour tomorrow. He said cabinet positions were likely for Mr Dunne and Mr Flavell, as long-time Government partners. However, any post for Mr Seymour was uncertain given his inexperience.
Mr Seymour said he planned to ask anyway.
"Oh sure, we'll ask, but it's entirely up to the prime minister. He's pulled off an historic achievement, winning an outright majority for one party under MMP, so we're just going to see if there's areas where we can add value ourselves," he said.
Mr Seymour said he was interested in working on charter schools within the education portfolio.
Mr Key said he had not ruled out working with New Zealand First leader Winston Peters, although he suspected Mr Peters might rebuff such an offer in favour of being Parliament's main opposition party.
Mr Key will also be having cabinet and caucus meetings on Tuesday and he said his message would be that he wants to avoid what he calls "third term arrogance".
He has also repeated a pledge he made on election night that National will not veer off to the right.
"We've hugged the centre ground over the last six years. Obviously there are some things we want to do; RMA (Resource Management Act) reform, employment law reform, but they'd be very much based around what's in the carry over provision ... what we talked about before we left. We're not looking to do radical, different things."
Mr Key is expecting that Parliament will resume in a month's time on 20 October, with new MPs being sworn in and the Speech from the Throne beginning the next day.