Developing a learning culture, one of continuous training, with your sales team will ensure that you are all performing at the top of your game. And, training works best if it involves lots of role playing. People learn best by doing.
I like to have my sales team learn and use scripts to guide their calls and demos. Burn them into their brains. Once they have them memorized, they can discard them and riff, but not until they have done so.
It used to be called the training manual. The sales playbook, which documents your sales process, scripts, demos, sales tools, giving your sales team the tools they need to sell. For an early stage company, probably the most important thing about a playbook is that you get organized writing it; its production forces you to think through your sales process systematically and document it.
As an early stage company, you are likely selling something new, different and somewhat complex. You need to continuously train your sales team on how to sell it, and work at continuously improving their skills.