Even though I had been in the creed for a long time, my trainer level is only 1.5k. I was wondering a good way to level up your trainer level, even if it includes spending coins- the way should not have getting another person to train it for you.

well the most common thing to do is have one of your pokemon get the skill "Toxic" so you can kill ur opponent's pokemon fast.

teach one of your pokemon toxic and battle against dark alley ....You can gain some good exp that way

First you have to complete all the gym badges to fight against mysterious trainer..! Buy toxic or loan any pokemon which has the move toxic from another player and then use megahorn to cause high damage to the mew...! Then keep on defeating him and you will get max experience...! Hope it helped you.