Role Playing: When you first introduce new messaging, don't train it by handing out a bullet list and talking through it. Get your reps comfortable with the messaging by acting it out in simulated prospect conversations. Some organizations go as far as to have a live role-playing "test" for new reps to make sure they're comfortable using new messaging. But even if you don't go that far, use role-playing to introduce messaging and then incorporate "refresh" sessions on occasion to keep it fresh and top of mind.
Don't Overscript It: Good sales reps are going to use a word-for-word script anyway. It's OK to give them messaging in a training environment that is written out - in bullet or paragraph form - but you can't expect them to use this verbatim in a sales pitch. It will come across to to the prospect as wooden, contrived and/or inauthentic. Instead, highlight in your messaging the key words and phrases that are most important, and use the role-playing to reinforce that these words & phrases are making their way into conversations.
Sell it with Research & Examples: Want your sales team to believe in the new messages? Prove to them that it's real and will work with their prospects by backing it up with research and outside examples. Give them confidence that these messages will resonate with their prospects and help them sell more.
Try a Conversation Tree Approach: When you structure new messaging for presentation to the sales team, consider putting it into a "conversation tree" format. In other words, map out the progression of questions or back-and-forth you'd expect will happen on the call. This will show reps not only what messages you want used, but how to contextually introduce them into a natural conversation.
Keyword Reminders at Each Desk: Even if you use bullet or paragraph-formatted messaging to educate & train the sales team, don't expect this same format will be useful when they're on a live call and need a reminder. Instead, give them something they can pin up at their desk that focuses on the keywords. If trained well, these keywords will remind them "on the fly" of the broader messages, phrases and themes they need to use on the phone.
Monitoring & Reinforcement: If you have the ability to do remote call monitoring, use these sessions to check for correct and consistent usage of the new messaging. Afterward, call out those who are using it well and anonymously cite examples where it may not have been used, with suggestions for how it could have been incorporated. This will reward those who are using the new messaging with some peer recognition, while providing an ongoing training opportunity without calling out those who may still be struggling.