First Things First
Higher levels mean meeting Pokémon with higher CP in the wild and getting Pokémon with higher CP from your egg hatches. So you'll want to get to those higher levels ASAP.
Now, before we examine how to get tons of experience points (XP) to hit those levels, we first need to understand what each action is worth. Above you can see the XP awards given in a handy table, as kindly compiled by the Pokémon resource website, The Silph Road.
As you can see, the highest amount of XP comes from hatching a 10-kilometer egg. However, that's not an easily replicated task. The next-highest award comes from evolving Pokémon and adding new Pokémon to your Pokédex, so this is what our guide will focus on.
Every Pokémon you catch or hatch rewards you with candies. When you spend candies to evolve a Pokémon, you'll get 500 XP every single time, regardless of the type of Pokémon you evolve, or amount of candies it costs. So, how do we use this information to our advantage? To do that, we need a little help from our pigeon friends.
You know all those little Pidgeys you've been avoiding? They, along with Weedles and Caterpies, are your ticket to leveling up. While these little creatures aren't very powerful, it only costs 12 candies to evolve them to the next form. Each one you catch gives three candies; four if you transfer it (i.e. trade your unwanted Pokémon for another piece of candy).
Collecting Pidgeys and being patient may be a challenge for some gamers, but if you keep them around long enough—"Pidgey Stacking" as we call it—you'll soon be able to reap the rewards of evolving them en masse.
Whether you acquired one from leveling up (levels 9, 10 and 15 come with Lucky Egg presents) or bought one from the in-game store, Lucky Eggs will double all XP you gain for 30 minutes. So once you activate this item, you only have half an hour to do as much as you can to get those double points.
This is when you start evolving those birds and bugs. Each evolution will now net 1,000 XP—or 2,000 if you're adding a new entry into your Pokédex. This means you want to save all evolutions for the Lucky Egg! If you managed to save enough Pokémon to evolve, you can easily get one or two levels closer to Level 20 in a single shot.
Gotta Find 'Em All
Organize your Pokémon collection in a clear way—and get those candies ready—to make the best use of your 30 minutes. It's also recommended to star all the Pokémon you plan to evolve, making it easier to find them quickly.
Be sure to transfer all the Pokémon you need to release before activating the power up. You don't want to waste precious time transferring during the double-XP period. Remember, you only have 30 minutes, so prepare wisely. Even if your game crashes, you're still on the hook for those 30 minutes. So block off that time and don't allow yourself to get distracted!
Patience Pays Off
What this means is that with enough evolutions, you can easily get tens of thousands of XP from Pidgeys!
Keep in mind it's not recommended to change Pidgeotto, the second form of Pidgey, to Pidgeot, the final form. The second-tier, 50-candy cost only offers 1,000 XP (2,000 if it's your first Pidgeot); yet, evolving four Pidgeys for 48 candies will net 4,000 XP, making it much more cost effective. Besides, you'll likely find a Pidgeot in the wild to catch, so making this Pokémon might be a waste of 62 candies altogether.
Reap the Rewards
Being patient, saving those weak Pokémon for evolution, holding onto new evolutions and using your Lucky Eggs at the right time is going to push you to Level 20 and higher in no time.
Save your candies and save those little bugs. The perks of achieving Level 20 alone are totally worth it!