When you are a startup with a MVP or a product with some traction, a lot of potential, but few paying customers, how to get the attention of a successful startup to build a strategic partnership?

• How to identify a successful startup that could be interested?
• Why would this startup be interested and what could be the deal / win-win?
• Who to call? What is the decision process? Average time before getting a decision? Should we approach several startups in the same field at the same time?
• Is it true that APIs and platforms can be useful? How and Why?
• Is there a contact which is signed? What is typical? Is there a need to have a lawyer to craft the contract? to negotiate?