My first tip would be to use the stock build you are given when you enter the mists. Here is the build and my take on it follows.
http://gw2skills.net/editor/?fcAQJAqelsp6ZnuSfF17IRoHF2wqV0D9bZK/pgcB-ToAA1CtI2RtjbHzOyds7MKYGC
This build is strong and will teach you some important fundamentals.
*kit swapping
*mix of offense, defense, and support
*heavy investment in Inventions and Alchemy makes this build tanky with a good variety of options
Kit Swapping:
The Bomb Kit is a great beginner kit. It gives you combo fields, conditions, crowd control, and in this build, some healing. With the trait Backpack Regenerator and Elixir Infused Bombs, you can easily tank a single opponent until help arrives. Big Ol’ Bomb also gives you a great tool for clearing enemies off of a downed ally, or pushing enemy players out of a control point so it can be neutralized.
Offense:
The combination of conditions from your pistol and the Bomb Kit will help you wear down opponents that have trouble cleansing conditions from themselves. Bomb Kit #1 also deals respectable dps on its own.
Defense:
Your traits and skills give you a lot of damage mitigation, healing, and condition cleansing.
Support:
You can heal your allies with bombs, buff them with tossed elixirs, and peel enemies off of them with skills like Magnetic Inversion, Supply Drop, and Big Ol’ Bomb.
Flexible Traits:
Depending on the enemy team you’re facing you can make adjustments to your Inventions and Alchemy traits to suit. If you’re facing a team that will be very heavy on conditions, Backpack Regenerator can be swapped for Cleansing Formula 409 to allow your Grandmaster trait to be changed to Automated Response. If you’re not facing many conditions, you can afford to swap out Cleansing Forumla 409 for Fast Acting Elixirs. If you see a lot of warriors and/or guardians on the opposing team, drop Reinforced Shield in favor of Stabilized Armor to help against their myriad stuns and knockdowns.
I’ve played this basic build in over 30 tournament matches. It does well on all maps and against the majority of professions. I have swapped out the Soldier’s amulet for a Cleric’s amulet. You do lose a few thousand health, but I find I prefer the increased healing over the vitality in most situations. The Soldier’s amulet is quit effective in this build however, and there’s no real reason to swap it out.
Next steps:
So maybe you’ve played this build and want to make some changes. The runes, sigils, and amulets can be changed to suit your needs without compromising the focus of the build. I would start there if you want to make some changes. You could also add another kit in place of Elixir B or S. I would recommend swapping out Elixir B. Adding the Tool Kit will make you more of a bunker, while adding the Flamethrower or Elixir Gun will make you more supportive. I would avoid using the Grenade Kit with this build as you have to go 30 into Explosives to really make them potent.
Some good candidates for runes are: Forge, Grove, or Dolyak.
Possible Sigils: Energy, Hydromancy, or Battle.
Amulets: Cleric’s, or Shaman’s.
I hope you beginners find this helpful.