Everything worth knowing, nothing that isn't.
Consent is mandatory
Promotional SMS may only go to recipients who gave marketing consent, and every message must offer an easy opt-out. This is both a legal requirement in most markets and a deliverability protection. See /answers/how-to-handle-sms-opt-outs and /answers/what-is-dnc.
Classify and register correctly
Promotional traffic is often registered under a separate sender ID and routed as its own class; mixing it under a transactional ID risks suspension. See /answers/how-to-register-sender-id and /answers/what-is-transactional-sms.
Make it convert
Identify your brand, lead with one clear benefit and a single call to action, time it to local business hours, and segment the audience. See /answers/sms-marketing-best-practices and /answers/sms-marketing-roi.