Come up with carefully-crafted agreements - Don't over-rely on boilerplate contracts. Make sure your agreements are tailored to each vendor. This requires some upfront work but it will help you maintain a smooth relationship later on.
Talk to suppliers even when you don’t need to negotiate - Check in with your suppliers regularly, even if you're not placing orders or negotiating a contract. Discuss the current state of the industry and talk about any priorities, plans, launches, etc. During these informal conversations, your vendors will likely be more relaxed and share information more freely.
Think of your suppliers as partners rather than just mere vendors - This may not apply to all your suppliers, but in some cases, it helps to think of vendors as partners that you work with, rather than third parties who simply provide products and services. Adopting a “partnership mindset” can help you strengthen your relationships, so you can work better together.
Invest in product forecasting and share data - This will help keep you and your suppliers on the same page when it comes to inventory management and allow you both to optimise the ordering and fulfilment process.
Be an excellent client - This sounds obvious, but you’d be surprised at the number of businesses that neglect professional courtesies. Things like strictly adhering to payment terms and being polite and friendly can go a long way in nurturing strong supplier relationships.