For mage, i'd focus on ENCHANTING as my core skill, almost exclusively until about level 10-12. The compensatory power of the enchants on weapons and armor, coupled with base destruction/alteration/conjuration spells, should easily get you through those early levels. When the game starts to require greater damage output and survivability of you, start putting as few perks as possible into the other schools in order to get the most essential abilities only. So, in my opinion, these would be Impact and Augmented damage in Destruction, and Mage Armor in Alteration. You would also get the mana cost reduction perks only when absolutely necessary, or as prerequisites. Enchanting, of course, can be used to create armor and items to help you gain mana/health, or use less mana, while also increasing your other magical skills, in addition to creating killer enchanted weapons if you're doing a battlemage (i might just use a few good staves).
For a warrior... hmmm... i think i might actually do SMITHING (see a pattern in the logic, here), although some have said it is very overpowered (sneak might be, as well). I'd perk smithing pretty much until about level 8-10, then go out with better armor and weapons and the rest of my skills without perks and let the quality of the gear compensate. After assessing combat effectiveness, i'd perk into other skills as needed, for example to reduce stamina cost of power attacks, or to unlock special abilities like shield bash, leaving the base perks at rank 1/5.
The key is finding that core skill that greatly facilitates everything else you'll be doing; sneak for stealth characters, and most likely enchanting for mages and smithing for warriors. At some point, you'll be rolling relatively smoothly with the solid core archetypal build and tight, focused perk spending (somewhere around level 16, at least for my stealther), and from there you should be able to start branching out into hybrid builds if you want, or just maximizing the archetype).