Know the difference, there are spells that does better in one or the other.
Learn that tanking does not exist in PVP
Learn that mindless charging can put your party into serious danger.

Most players start mesmers for PVP, however if you plan to start a mesmer for
PVE, brace yourself for many grievances. (Not being invited into parties is
an example)

IW isnt very reliable in high ranked organized PVP. Guild vs. Guild,
Heroes Ascent, or sometimes maybe even Team Arenas. These are the areas where
enchant stripping is very common

Its best to make use of axes withteh skill cyclone axe in PVE rather than
sword for AOE damage. Increases your DPS albeit spread to several targets.

Read number 3 in the IW Mesmer-Specific Techniques and Information section.