Strategy time for a random Pokemon. Today's Pokemon is... Garchomp the once overused Pokemon (I mean that in every way). This Ground Dragon was the king for about a year until everyone realized it was too good and moved it up with the legendaries.
Generally speaking, this... Garchomp as they call it is another name for the Pokemon version of Bruce Leonardo DePinchme (which can still be beaten by Chuck Norris).
Every Garchomp should have Earthquake, with no exceptions. Having a ground type like Garchomp without Earthquake is like a cat without fur- it's not powerful, and it's not even cute.
Here is the standard Garchomp summarized in one set with a few options.
Dragon Claw / Outrage
Fire Fang / Overheat
Item: Choice Scarf / Choice Band / Yeche Berry
If you have a Choice Band Garchomp then maybe you shouldn't go with Overheat over Fire Fang. The Yeche Berry is sort of a trick to barely survive an unboosted Ice attack and continue to pound legendaries or foolish overused Pokemon who dare to challenge you.
There are few major counters against this annoying land shark, except a few water-type tanks like Slowbro or Milotic. All you have to do is beat him with a burn or an ice move. Very often Garchomp is stuck to a move, use that against it. A legendary that's faster than it can shut it down, hopefully switching into a weak attack like Fire Fang.
Altogether Garchomp is just a cheap Pokemon like Shedinja that shouldn't exist.