You are not getting better in pve you just try again and again, learn every single second of the fight and the stuff you get every week do the rest.
In pvp, each arena is different (assuming you are not wintrading xD), sometimes you learn something, sometimes you just trollface opponents but you get experience and you learn every mechanics of your jobs and the others.

In pve, the best way to get highter dps is stuff and positionning. More you try and more you learn where to be and when. More you try and more you get stuff since every weeks you get some gear.
Pvp was fun when i was i70 playing with i70 mates vs some R30. I lost a lot of game but win a lot of xp. Since 2.2 we can't even fight other R30, matchmaking is totally a fail, matching 4 R30+ vs unknown R0 xD