My first GW2 level 80 is an elementalist, and my current trait build is based around Elemental Attunement. This embraces the dissociative identity disorder that is the elementalist class: this character does not take a role, instead cycling through them as fast as skills recharge. If the point of my class is trying to use 16 skills plus 4 different auto-attacks as efficiently as possible, darn it, I am going to cycle attunements madly. I just need to figure out how to mix in a little more earth auto-attack for bleeding. I usually use a scepter and focus, switching to a staff for most WvW and purer support roles.
I have 30 points in arcana, so I get +30% boon duration and +60% attunement recharge rate. In any serious fight, I will be flipping attunements as soon as I run out of non-auto-attack skills in an element, which usually means something like 2-3-4-5-1-2-switch-repeat. It takes 3-5 seconds to use all the spells I want in an attunement, so I try to cycle through them every 15-20 seconds. Elemental Attunement means my group gets a boon every time I switch. The group should continuously have at least 1 stack of might plus 1-2 other boons, while the enemies are on fire and blind. Eventually, I am going to start hitting F1-F4 properly while doing this, and maybe I will even remember to use F1-F4 properly on all my other characters someday.
For other traits, I consider at least 5 points in air required and preferably 10 for One with Air. I want to move 25% faster, so I live in air attunement when not doing my combat cycle. I also keep 30 points in fire as my damage source. In solo PvE, fire is my damage. Once we have fast trait-swapping, I will probably go with 30 water for a support role. +damage per boon is nice, and every time I cycle through water I will grant everyone healing, regeneration, and double condition-removal (assuming Cleansing Wave and Cleansing Water stack).