The key to a successful partner model is that you act as partners! That is, you both contribute more than 50% to the relationship, ensuring that you put in the effort at the things you are strong in, and that the partner does the same. A successful product partner operates in an environment where they are more effective at dealing with the customer directly than the product vendor is themselves. This could be that they are geographically closer, operate in the customer's industry, already act in a consulting role to the customer or any similar circumstances. The partner however realised that they cannot make their own product, or even if they could, that yours fits their needs better and is a better overall solution.
Once a good potential partnership is founded, the next step is to design the overall solution. This could be as simple as fitting the products together for an early opportunity, and removing any points of overlap, by deciding on the roles and responsibilities. It could be that the solution contains technology from one side, and implementation know-how from the other. Early presentations to customers need to communicate that this solution is holistic and consistent, and see that the strengths of both sides are being used.
It is vital that both sides of the partnership understand the same key benefits to the customer, and are able to describe parts that the other side is providing accurately and truthfully. A larger amount of prep time for any meeting or demo is called for - and if technical integration is going to be shown, ensure that enough time is spent to put it together. This could mean visiting the other partner before demonstrating the product to a customer so that all things run smoothly. A dry run is highly recommended with all meeting participants. If any problems exist in the demo system, everyone needs to know how to avoid showing them!
Follow up from these early meetings is also important. Keep in touch with the partner, even if it is just a courtesy call every week or more often to check for feedback from the prospects, and check further opportunities and business. This should be done on each level of the business, so your Partner manager to their partner manager, your sales rep to theirs, and between SEs or technical equivalents. You will be amazed at how often different kinds of information filter through differently on the levels.
Once the early deals come in, the partnership should then grow and be nurtured to the nirvana of partnership, where each side of the relationship can bring in business on their own.