I hate to be the one to tell you this, but mesmer is easily the most miserable class in the game to level (next to engineer). What others said about it not picking up until level 40+ is correct. Expect to suffer until then. :P Mesmer is quite possibly the most heavily trait dependent class in the game, so until you have substantial trait points to place it's going to be painful.
Having said that, once you get to level 40+ they are OP as Hell and totally worth it.
I also don't suggest using scepter to level. The DPS is terrible except for the #3 skill. I don't recall shattering being very effective at low levels either. What I ended up doing (which I learned from one of zito's builds/posts) was the following:
Equip 1H sword + focus
Gather mobs (however many you're comfortable with)
Lay down an Ethereal combo field (this can be done with staff #5 prior to getting the slot skills Feedback and/or Null Field)
Cast Phantasmal Warden (they have a whirl finisher when paired with the ethereal field will cause them to do Chaos Bolt projectiles)
Use sword #2 ability (Blurred Frenzy allows you to evade attacks while it's active, which means you can get temporarily tanky)
??? (if they're not dead after that then I'd usually dodge away, weapon swap to greatsword, cast Phantasmal Berserker, and otherwise auto attack what's left)
I have no experience with condition builds for mesmer though. I always found staff to be more of a defensive weapon, so outside of ability #5 for the combo field I didn't use it that much. This would just be my suggestion for less painful initial leveling is all. Like I said, once you get some trait points you'll have a lot more freedom with effective playstyles.
Personally, I did not find Engineer or Mesmer to be overly difficult or burdensome to level. Both were as quick as the other professions. Noting Ranger and Warrior are like the two fastest/most powerful professions in the game.
I did find Mesmer to be poor at mass mob farming. Though the Engineer excelled in this regard as few sans Ranger.
Weapon Choice: Sword MainHand/Greatsword/Staff are all you should use early on until you get used to the class.
Sword Mainhand - Hits fairly well. Aprroach your target or targets with Illusionary Leap, then use the swap to teleport to the target and snare the target. Follow with Blurred Frenzy (Skill #2). Blurred Frenzy is one of the best early game skills you will get. Hit with your 1 attack combo and dodge out when things get rough.
Greatword - Once at range, drop iBerserker, with Mirror Blade or Stab for single target versus aoe hits. Spam 1 as its a beam attack that passes through targets. So if you have multiple mobs, target the furthest away and it will damage any enemies between you and that target. Use Wave to knock foes back and give yourself breathing room.
Staff - Staff is good if you learn to kite. Feigned Escape (skill #2) is a good escape move. Consider it a third dodge and a clone factory. Staff works well in groups early on as you can drop Chaos Storm on the large mob concentrations without aggroing a ton.
Off Hands - You're two best off hands are Pistol and Focus. Focus seems like it sucks early on, but the pull gives you another interrupt, and the Warden is good AoE. Even at early levels, you can hide within the whirl of the Warden's axes to be saved from enemy projectiles. Pistol does good damage at all levels, fires off fast, stays alive because its ranged, and has another interrupt.
Notes: As you can see form my advice, Mesmer Survival depends on illusoins, illusion management, and interrupts. Mesmer is a multi-tasker's class. You're hiding in warden to reflect projectiles, but sent out a sword #3 clone to a ranged mob so you can teleport to that mob. You get there, blurred frenzy, shatter, kill it, Look back behind you at mobs coming and Greatsword 5 to interupt/knockback, follow with Berserker and cripple them. So on and so on.
Stats: Early on, go with power and precision. I don't feel condition mesmer is viable until much later on, and furthermore, I didn't feel it was all that viable until they released Rune of Perplexity. Your confusion condition will suck in PVE until you get extended condition duration. (That's where traits and Runes of Perplexity come in.)
Utilities: Your best utilities are clone creators like decoy and mirror images, along with glamours. Mirrored Feedback is awesome. Like the warden, but it reflects back projectiles. You can aggro from a ranged mob pairing by just dropping this on them. Blink is also very useful, though I'm not sure how good it is early on. Blink is a movement booster, and an escape.
General Playstyle: Multi-task your illusions and move. Dart in and out. Mesmer is movement reliant while not having a lot of access to swiftness. Once you get rolling with mes, you'll be darting in with sword and shatters, leaping back with staff or blinks. Use your reflects and knockarounds to manage terrain.
How would you recommend managing illusion shatters. Is it 3 then wrack/confuse if it is up (will that gimp my damage if I don't let the warlock/beserker do his thing for a little).
Illusion management depends upon your build.
If you have traited for shatter damage, its best to shatter right away. However, Phantasms follow different rules. Generally, you always want your phantasm to fire off its attack before shattering, even if you are a shatter build. Clones you can shatter right away with little loss.
This is a harder choice. Your Phantasm Build does the most damage with three phantasms up. You can decide to keep these up without ever shattering and you will be fine. However, there are often moments where both of your weapon-based Phantasms are off cooldown. At these times, you can hit a shatter and then immediately bring out your two phantasms afterwards for a short boost in damage.
Many condition builds use Phantasms that do channeled attacks that trigger bleeds from traits. This makes Phantasms useful to keep up, but it also makes certain clones useful. Greatsword clones and Staff clones can apply conditions. GS clones because they channel their attack and can crit. Staff because they apply condies and boons.
You can also add conditions to your shatter effect. However, I feel that going for a confusion shatter build applies less confusion and conditions than a simple iDuelist shooting through a chaos field does. If you use Cry of Frustation to boost Confusion for a moment, it works much like a Phantasm build shatter. Do it when you can bring illusions right back up again because they are off cooldown.
You generally don't shatter unless it's distortion. These builds often use the trait that gives you 3% less damage recieved per illusion up, so you want max illusions up at all times. Also, the more illusions you have up, the more targets you have for others to attack that are not you.
General Rules on Shattering
-You want to use Mind Wrack or Cry of Frustration with max illusions up. This is always best.
-Diversion shatters gain little from having more than one illusion up. It's completely fine to use one single clone to create a Diversion shatter and interrupt a foe.
-Distortion is an oh-shii button. This means it can take priority over all these other rules. It gains an extra second for each illusion up, so it works best with max illusions. However, if you have no escapes, and no heal, then you are hitting distortion no matter how many illusions are up.
-It's better to not shatter a Phantasm while it's channeling attack. Many times its a loss in dps. Wait a second for it to finish.
Phantasm Specific Rules
Warden - This is what you sit inside if you are hiding from projectile attacks. Sometimes you would rather have it up for that purpose rather than shatter it just for this reason.
Defender - If you are using this, then you're worried about group damage. This means you are never shattering this Phantasm. Once you shatter the Phantasm, the group damage reduction it gives goes away. So just keep Defender up unless you have an emergency Distortion situation.
Enchanter - Rarely used, but like the Defender its purpose is greater than its shatter. It removes conditions from your group and boons from your foe. You keep it up for this purpose. HOWEVAH, it has a low cooldown so shattering it is not as big a loss.
Swordsman/Warlock - This rule is a bit iffy. These two have lower cooldowns, and they attack quickly. This means that they can often be popped, have their attack hit, and then shattered even in a Phantasm build. This all depends on your cooldown management and weapon swapping. I am just including this note to say these are the two Phantasms I shatter quickly most often.