The more you offer the more you need to tie it to deliverables.

There are limitations on what a person can do without a license to raise money on contingency but you can set goals of X number of introductions to venture capitalists as a criteria for earning equity.

I tend to like offering 1-3% to a really accomplished person if it's very early and they can commit time to the company.

If it's later stage 0.25 - 1% is more common.

You can also pay an Advisor with cash and lower the amount of equity.

What do you need this person for?