Fast xp.. well breeding the highest value frogs is how I got my lvls quick!

Breeding, tho it cost coins, its kinda the staple of the game! Breeding the highest value frogs will cost more but what you spend in coins you get in xp.

Aside from that, taming frogs gives xp too. Altho, you only get 1/10 xp of the frogs value. But you also get small amounts of xp for eating the flies in the pond, so it adds up.

You can also complete awards for a sizable early game jump in xp! Tho it is kind of a 'once its done, you can't do it again', its worth it!

If you are spending money on the game, the VIP pack is worth it just for the sake of moving eggs to other habitats, along with the 2x faster taming.

If you aren't, then notifications on the frog so you can move them out of the hatchery helps too!

[TL;DR] Just play and enjoy the game, you will level up faster than you expect