I am a firm believer in hiring professionals to do a professional job. We have worked with dozens of freelance videographers and helped brands achieve some sharp marketing videos.
So some tips:
1) Hire a freelance videographer and writing team. Developing a story board is not easy and there are brilliant writers just waiting for jobs like this.
2) If you are going the DIY route make sure there is a beginning, a middle and an end to your story board.
3) Use humour where possible.
4) Keep the script short and attempt to get your message out in the first 30 seconds.
5)Speak directly to the audience -so know really well who that audience is!
6) Find the right tone depending on your company brand and mission.
7) Tell a solid story. So you want to start by presenting a problem, introducing a solution, then explain how it works, and lastly create a call to action for your target audience.

Hope this helps. I'm here if you'd have further questions.

blue skies,
Daniela

Hope this helps

I'm been running a promo video animation studio for the last 4 years and worked with hundreds of startups.

The conventional formula for a 90 second demo video is as follows.
1. Problem -> 2. Solution -> 3. Call to action

1. Problem
Briefly explain what pain your product is solving.

2. Solution
This is where you explain why your solution is so awesome.
Explain how your product/services addresses and solves this problem.
List 2 or 3 benefits/features that make your solution special and better than anyone else's.

3. Call to action
Make sure you end the video telling people what to do next.
Either visit your website, download your app, or give you a phone call

For a 90 second video your script should be around 240 words or less.

Try not to sound too corporate and add a least one moment in the video can put a smile in your audience.

A successful demo video will be watched all the way to the end so make sure it's fun to watch.

I actually produced an online course where I explain the exact process of producing animated demo videos and it's now been taken by over 5000 people..
It's 10 hours long and covers script writing, storyboarding, illustration, animation and sound design.
You can check it out here: http://bit.ly/1eTlZ0Y

Please let me know if you have any other questions.

Cheers,
Miguel

There are too many things to consider as “guidelines” but what you want to do in a high-level should reflect the the brand position and brand promise.

1) Figure our your brand story and how to tell it
2) Develop an outline for the content/script
3) Create a storyboard to communicate the brand story
4) Hire necessary help in creating the video (talents, voice over, animator, videographer/photographer, and a creative agency)

Unless you are a brand expert, I would recommend hiring help for step 1.