You should net this trophy pretty early in the game. After you choose your character and load in for the first time, just follow Claptrap to learn the basics of the game. After facing off against a few bandits you’ll fight your first boss, Shiv. As soon as you complete this fight, you will gain your first level and pop this trophy.
Also good to note is that you unlock your Action Skill as soon as you Level up letting you try it out super early in the game compared to their other mainline entries.