My biggest tip for WvW is to consider surrendering shortbow for S/x as precasting Infil Strike and swapping before getting into combat via steal gives you a disengage + cleanse if you need it without needing to burn Shadowstep or others if you start losing.
It pretty much boils down to learning other professions and knowing when you can hit them and why/how, and to always have an out. Rev’s auto-taunt and similar passives can kill you on engage if you don’t immediately do something about it. You need to be faster than your enemy at all times and always be evaluating what they’ll do next while making the best decision possible as to how to deal with it.
In essence, only practice can make you a good thief, because it’s mostly dependent on how you play in respect towards your enemy.
Thief doesn’t combo (aside from a few select builds) or have any rotations like most other professions. You play it as you need to. The first thing you can do is to know your kit (whichever you pick) inside and out such that you can cut down a lot on the active strategy of thinking of what to do and when. You’ll figure it out in time. Eventually responses to certain things will become second nature. With enough practice, you should be able to have a pretty familiar idea what your cooldown states should be without looking at the abilities themselves. This is essential when playing out-numbered or against persistent enemies; as someone said above, it’s critical you always are looking 360 degrees around you and into the distance, maintaining enemy locations and their subsequent cooldowns. It’s more important you pay attention to them and what they’re doing than trying to fuss over what skill you have and giving them even a fraction of a second advantage. Once you get your flow down, you’ll be able to pay total attention to your enemies, capitalizing on any opportunity you can to attack, while using knowledge of your limits and the unknowns of their kits to best-determine how to act.
The thing about the thief is there’s very little advice to be given without getting into specific play habits via video analysis. The subtle nuances are what define good thieves from bad ones. Find a weapon set you love, and just play it to death. Learn it inside and out. Recollect on every death, look at the damage logs, and ask yourself why you died, then think on what you could have done to not have died. Re-evaluate your build slightly if you need to if you consistently lose to something for a specific reason. Apply your knowledge, rinse and repeat.
