I'd just focus on gathering pidgeys, caterpies and weedles as they only need 12 candies to evolve, also zubats. Store them all up until you have around 160 candies of each, plus 10-15 of each pokemon in your bag. Pop a lucky egg and then evolve everything within that 30 minutes of double xp, each evolution will be 1k experience and you shoot right up - its the most efficient way to level!
A 30 minute evolving stint with a lucky egg can easily net you 40-50k experience, and you get given new eggs at certain levels so you can hop from threshold to threshold, only being held back by needing to collect all the pokemon and candies beforehand
Once you've hit a high trainer level (around 15+) you'll start to see naturally-high pokemon in the wild, like 500 CP and above - catching those will mean you spend less resources on leveling up weaker pokemon caught back when you were level 5-10, I've only just started to power up pokemon and I'm level 17
edit: re: powering up pokemon before or after evolving them... I have no idea would love to know if anyone's experimented! It seems evolving increases CP by a multiple of the original pokemon's CP, influenced by whether its a 12, 25 or 50 candy evolution.. part of me thinks we should be powering up pokemon to their caps before evolving them for the greatest multiple, but I'm not sure