Since the appearance of Pokémon is totally randomised in Pokémon Go (with factors such as time of day, location type and nearby landmarks all making a difference), there's a good chance you'll have the opportunity to catch more than one creature of the same type.

Naturally, you might be inclined to avoid wasting a Pokéball, but having duplicates has its uses. Extra Pokémon can be traded to Professor Willow for candy, which helps increase the stats of your best Pokémon and even helps them evolve. To do this, click the Pokéball icon, select 'Pokémon' and hit 'Transfer' by the Pokémon you want to drop.

During your time with Pokémon Go, it's likely that you'll encounter more than one of the same Pokémon. If you do get a chance to capture a Pokémon you already have, take a look at the moves the wild Pokémon has (listed in the Pokémon's information screen after you've captured it) - they may have a better move set than the one you already have. If that's the case, then remember this tip: capture the new Pokémon, then trade your existing Pokémon for an instantly-better fighter. It's ruthless, but that's the world of Pokémon Go.