Here are things you need to do if you wanna be a good pokemon trainer
1:Make a team that has a good ability/s you ned to have all 6 pokemon to have different types
2:Ev/and or try to iv ttrain it theres a guide on the other page on how to do so
3:Try to have a status condition that will make it harder for your opponent to win lie if u use will-o-wisp theres a good chance that ur opponent wont be able to move so you can attack him without him/her can attack you especially if it has a 100% accuracy of hitting but make sure you dont use it on the wrong pokemon some pokemon can absor it to gain att. or hp or it wont be effective to them
4:Make your pokemon have all differnt types of the move
5:Try to use status moves which can boost attack like swords dance then you can attack him with alot more power
6:Try using moves that if it hits it has a chance or gauranty that it will inflict a stat or status problem
7:You can use hp and or status recovery moves that restrore hp or burns/paralys etc....
8:Change weather to power up your pokemons move
9:You can use tm/hm/egg/move tutor moves to help you out get good moves
10:You can use abiities to raise att or help you stand on ground with defense
11:Use items to power up attacks/def/speed etc....
12:Some Pokemon are better in double or single battle depending on what they are good on is depending on what its move can learn like electivire can use dishcharge a good partner would be jolteon cuz its ability is volt absorb which will let it recover hp 13:Always try to use pokemon moves that are very effective against to your opponent if u dont know hat move to use for its weakness check out the pokemon weaknss chart