Before I reveal this not-so-unkown secret, let me tell you the recent updates for the Season 5 of League of Legends.

Update 5.1 for Summoner Spell Smite:

Smite now stores charges up to a maximum of 2, but has an internal cooldown of 15 seconds so you can't do silly things like double Smite things.

Right now, Smite's a pretty important ability for a lot of reasons (securing buffs, smiting other folks, farming the jungle), so we're seeing most junglers start to 'hoard' their smites as the game progresses. When you think about it, that's a pretty significant chunk of cool things a jungler misses out on (as long as Dragon or Baron are up), so we looked for potential solutions.

Like Smite charges.
NEWCHARGES Has 'em. Smite now gains charges at a rate of 1 per 60 seconds with a maximum of 1 charge at any time ⇒ 1 per 75 seconds, with a maximum of two Smite charges at any time.
NEWA COMPLICATED START Smite starts with 1 charge and only begins to gain additional charges at 1:40
NEWNO DOUBLE TAPPING Smite now has a cooldown of 15 seconds

As you can see, you can now charge up to two smites at a time with 15 seconds of cooldown in between. This information is crucial, keep it mind. Finally, remember the Ranger´s trailbalzer upgrade for Hunter´s Machete? Remember the heal it grants when you smite? Yeah? Lets proceed then

Any kind of jungler champion can be used for this trick, but junglers with a heal or high defense work best, like REngar, Vi, Poppy, Lee Sin or Nunu. Nocturne works especially well.

Start normally on your jungle route, but make sure to smite immediately the first monster to get your Smite as early as possible.

Keep on jungling and when you reach level 2 or 3 (When you have 2 smites stored) Recall and upgrade your machete into Ranger´s Trailblazer. If you have enough money, buy health potions and head to the dragon pit to prepare for battle.

Try to ward and to defeat the Scuttle crab just in case someone wanders by.

Start fighting normally, like you would normally do, activating abilities when possible and dealing the most damage as possible.

The trick here is to activate your health pots, if you have them, to get a better chance of success.

Look out for when your health drops. As soon as it drops below 60%ish, smite the dragon to regain some health.

The key to your success will be your second smite, which will be available in 15 more seconds, use it again as soon as your health drops once more.

If donce correctly, congratulation, you have slain the dragon at Level 2 (or 3).

Recall and change the jungler enchantment if you so wish (remember changing enchants is now free) and keep playing with a huge advantage.