When you evolve a Pokemon, its CP circle stays as full as it did before.
As a result, it really doesn't matter in which order you boost a Pokemon. However, you should keep a few points in mind:
- Powerups cost more Candies the more CP a Pokemon has (based on family boundsa Pokemon's level).
- Powerups cost more Stardust the more CP a Pokemon has (again, based on family boundslevel).
Cost will increase every second powerup.
Therefore, it makes sense to power up a Pokemon until it is near the upper end of your CP ring. As the ring stays in the same place, it will give you a rather decent CP per Candy ratio.
For example, if a Pokemon's max CP was 515 and it is currently at 425, it would make sense to power it up to 500 or more. At that point, you should evolve it, provided you have the candies.
Overall, you'll still be using fewer candies because you're doing most of your evolution on the lower side of the scale, and using the Evolution mechanic to sharply spike the Pokemon's CP.