"To become rich, you must be an owner, and you must try to own it all. You must strive with every fiber of your being, while recognizing the idiocy of your behavior, to own and retain control of as near to 100% of any company as you can."
"Never never never hand over a single share of anything you've created or acquired, if you can help it. Nothing. Not one share, to no one, no matter what the reason, unless you genuinely have to."
"Ownership is the only thing that counts."
In theory, investor dilution shouldn't matter. If you have 50% of a $10 million company and $5 million is invested, you now have 33.3% of a $15 million company. In fact, due to intangible benefits of the investment (mentorship, connections, prestige) you should be coming out ahead. In practice, this obviously isn't always true-- because no one knows what the true fair value of a company is, and giving up control can be disadvantageous-- but it is often true. Turning down, say, Y Combinator because 100% matters that much more to you than 94% would just be stupid.
Would you rather have 100% of $1m, or 50% of $1b?
The real test here might to only give part of your ownership away unless the party you're giving it to will make your remaining shares worth more than all of them would have been without them. In other words, if you give up 20% of a company, make sure they make the remaining 80% you have worth more than the 100% you used to have.
You should give them a vested share amount equal in proportion to the amount of value you feel they will add to the company. This is usually a variable range (and it varies), but something along the lines of: Every new developer adds .25% of value to the company minimum. Higher caliber people in the same position will add .35% of value. So your equity range, per developer, will be .25%-.35% (in this example).
Give stock in compensation for calculated value add. As you move through stages/growth, the value-add of each new employee will (should!) diminish if you're doing everything else right.
.35% was my example, based on rough memory of a prior startup. Your mileage may vary. Void where prohibited by law..
And of course, all equity should be vested, with little or none granted up front. Virtually no employee adds value the day they arrive, thus they should not have any stake in the company at that point.