Why You Should Save Candies

 The reason you should be saving candies, and even catching every Pokemon you come across, is not only because it's a good source of experience when you evolve, but because you will also find better CP Pokemon the higher level you get. If you went around catching everything or mostly everything, you will hit level 20 before you know it without having to evolve any Pokemon. People who live in rural areas may have a harder time (like myself) because Pokemon don't spawn as much and there is next to nothing for Pokestops.

The best Pokemon to be catch unfortunately, are Pidgey's, Weedles, and Rattatas. Not only are they common but they use little to no candies to evolve. If you can get your hands on a Caterpie catch those too. Pidgey's, Weedle, and Caterpie all take 12 candies to evolve, making the more viable than most other Pokemon when using the lucky egg and evolving method. Rattatas and Eevees both take 25 candies to evolve, and still are easy to stock up on the candies for the lucky egg. 

The level I would start using lucky eggs and candies at would be level 15. This is because though it isn't hard to hit level 20 it still is more time consuming than the first 15. If you are wanting a strong Pokemon over levels then you should wait until level 20 in hopes of finding a much higher CP.

When you use the candies to evolve it is also better to keep the candies of Pokemon you can evolve into something new for your Pokedex, but only evolve the Pokemon into the 2nd evolution. It is a waste to get the 3rd unless you are trying to fill out the Pokedex. You should try and save as many new 2nd evolutions as possible, this is because when you use a lucky egg to evolve everything. New Pokedex entries give 500 experience and so does evolving. Use a lucky egg those both become 1000 experience and 2000 when adding them together. 

Once you get a good amount of candies pop a lucky egg and begin evolving. I'm not sure how many Pokemon you can evolve in the duration of the egg, but more than likely you won't have enough time to use all the candies. Before you use the lucky egg though I advise holding onto several of the Pokemon you plan to evolve. 

It won't take long to get 100+ candies. You get a total of 4 candies per Pokemon, 3 for catching it 1 for transferring it. The process may seem slow at first but once you get use to it, it will be hard to believe how many candies you have.