Start with these four simple techniques:
* Be Proactive and Responsive
* Be Communicative
* Provide Choice
* Be Thankful
Providing options for customers who might benefit from an advanced version of a product or service, or from a product that would supplement the use of their main purchase, is a great way to provide value (and gain an extra sale in the process).
But, again, if you push too hard to upsell or cross-sell your customer, they might walk away without even making the original purchase they planned on making.
You can find more effective sales techniques in this blog: https://www.fieldboom.com/blog/sales-techniques/.