I'm going to have to disagree with you guys on Nightblades. Some of the strongest PvP players are Nightblades, dishing out over 20k damage in a single attack.

I'd say it's a class for players who are good at managing the minute details of a character's stats, since all of their abilities need to be perfectly in sync.
Echoing Grits, start crafting and researching traits as soon as you can. It can take a while to level it up but I'd say it's essential to be able to craft your own high level gear sets. I'm
still trying to do trait research, because I ignored it for ages.
Visit stables and level up your riding skills every day, even if you don't have a mount. The skills applies to all mounts that character has or will have, and once you get a certain number of points in each category your mount gets aesthetic upgrades like armour and saddlebags!
DON'T SPEND CROWN POINTS TO RE-DO YOUR SKILLS AND ATTRIBUTES. Took me several months before I realised that some cities have shrines which can be used to reset your skill and attribute points using in-game gold rather than buying those reset scrolls from the crown store.
As an extension to the point above - Don't be afraid to try new abilities and skills, since you can easily reset your points and rebuild your character with the abilities you've tested out and enjoyed. I can't tell you how often I've overlooked a skill for ages, only to find it to be essential to my play style further down the line.
"If more of us valued food and cheer and song above hoarded gold, it would be a merrier world."
"...a quotation is a handy thing to have about, saving one the trouble of thinking for oneself, always a laborious business."