Da Mesmer

First, english isn't my native language, so forgive me any spelling mistakes

something you need to remember at all times: STAY ON THE BACK!!

The mesmer is an all-offensive class and so has very little defence and only a few defensive skills, the best known is distortion, giving a 50% block for a few secs. As a mesmer you should prefer a player group over an NPC party, because in an NPC party, you give the directions and unless standing still and having brought a few wars, u'r in the frontline, and u should be on the back.
Probably the most potent chain in the game belongs to the mesmer: Signet of Illusion, Arcane Mimicry and Arcane Echo will copy any elite, preferably from another class, and have it use your illusion magic rank (should be 16), this way, u only ever need illusion magic and fast-casting for interupts (both yours and the enemy's). A few healing skills are always recomended, though put a number above a regeneration arrow, as your armor is weak. A "good" thing about mesmers is that playing them is very cheap, almost all of their runes and insignia's are only 100g, and unlike other classes, mesmer armors are only 'sets' because their name says so, visually, mesmer armors can be put together from different 'sets', giving armor a wide variety(on my pic, i have asuran boots(elite), stone gauntlets(elite), ancient attire(body, elite) slim spectacles(elite) and istani leggings(reg)(I've been saving for it for a very long time, others got 2 elite armors in the time i saved up for this 1). When u buy an elite armor, make sure u have at least the elite mask, body and boots, leggings and gloves are very often overlooked and so are optional, there's nothing wrong with buying them of course, but most pple only look at the body, the mask and the boots.

Mesmers have 3 main ways to choose from(there are others, but there are the ones used mostly), shut-down, Pressure and Interuption.
Shutdown mainly uses Domination skills to punish foes for using skills(Backfire, Vision of Regret), attacking(Empathy) or even for doing nothing (Wastrel's Worry). and some energy-stealing skills from Inspiration Magic.
Pressure means lots of Illusion hexes to make ur foes panic(or try to do so) by putting them under the heavy pressure of health degeneration, slower movement and/or damage over time(not-degeneration-damage). Hopefully, the enemy panics and does what u want him to do, make stupid moves, waste lots of energy on healing or using a certain type of skill.
Interuption doesn't need an explanation, does it? use fastcasting and inspiration magic.
Speaking of inspiration magic, this is the only source of defence and healing for the mesmer (apart from secondary prof-skills).

Mesmers have everything they need with them, so a secondary prof is often left as it is, the occasional spamable skill like a necro's Necrosis or anything alike is fun, but generaly, mesmers have all they need, EXEPT for 1 thing, a bodyguard, MESMERS NEED PROTECTION. a warrior is a must for a mesmer, they(mesms) are very fragile and need protection from all danger, as mesmers count on themselves being left unharmed and unchecked. But unfortunately it is not a rare sight that foes switch targets from the war, to the mesm, when this happens, give it a full spell-beating and run.

Mesmers are a blessing in PvP, but the masters are in PvE, as the mesmers can use SoI to fuel title-bound skills to (beyond??) their maximum, getting a (massive) gain over other profs. Passive effects(like more energy in asuran territory) are only affected by the title rank though.

Feel lika a massive spamming build, use Lyssa's aura and u'll never have to worry about ur energy ;P