I think the most important thing is to determine with which charity you want to align, and how that aligns to your business purpose and values. For example if you’re a real estate company it might be a stretch for your customers to understand why you’re aligned with pet rescue, however it might be easier for them to understand
the connection vs. something like contributing to the prevention of homelessness.
Once you’ve determine which charity fits with your brand and your company purpose and values, think about how you want to contribute. Will it be a % of your profits, a $ value for every transaction, allowing customers to round up their purchase, or donate after their purchase from your site etc. Quantify what you think the impact you can have will be (ie will this be hundreds or thousands of dollars).
Once you have that information, I’d do some research and reach out to a few players in the space you’ve chosen as your charity industry of choice. I’d ask them really pointed questions about how they would use your funding. Does it go directly to the cause, or will it be used on administration? What % of charitable donations do they take as administration fees etc. With which other organizations are they affiliated? That will allow you to make an informed decision on the best choice.
Once you’ve determined the logistics of how you’re going to collect and disperse additional funds to your chosen charity, then I’d recommend a joint public relations plan to announce your partnership. That way you can both leverage each other’s audiences for your respective businesses, and further cement the relationship. This can take many forms, including traditional press media, emails, combined campaigns etc.
I hope this helps~