Hi, it looks like this post is a couple years old, but in case you are still looking for advice, here's mine. :-)
To put it simply, confidence, clarity and knowledge.
To be more detailed - you need to know what you are looking for in a partner, what you expect from them, and what you are willing to offer, as well as what they NEED. This is particularly important when dealing with large companies as they will naturally try to position themselves as being the larger contributors and therefore that they should receive more in the deal. What you need to remember is; They are in this meeting (or in this case - they came to you), meaning they see a benefit or you have something they want. Doing the research to uncover what they want can help you gain the confidence to stand firm during negotiations.
At the core, strategic partnerships are negotiated similarly to a sale, with both parties trying to get the most out of the deal. However, by asking the right questions and doing the right research, you can avoid this feeling like a game of tug of war, and turn it into a positive, mutually beneficial result.
Other than the above preparation, you should of course have hard copies of the facts and figures to back up what you can offer and the benefits the partner will receive. My practice has always been to pitch the benefits before the requirements or the 'ask' as, if you position things right, the benefits can have them sold before you reach the cost.
If you are still having trouble with this I do actually run calls on this specific topic as I worked on strategic partnerships for 5 years in Canada and the UK for a variety of clients. It would be great to talk further and I'd be happy to help as leveraging partnerships is a particular passion of mine. :-)
Of course, if not, then I wish you all the best with securing strategic partners and hope the meeting went well.