R/N could use some help

I'm just a bit confused. I have been playing for quite a while but don't really know what the hell Im doing!

I'm playing as a R/N and obviously have quite a few skills that will interrupt a caster, but Im never sure when to use them. I mean how can you tell when they are actually casting? Do they do a different animation or something or do you just target the mesmer and fire away?

Which brings up another question I have. If I hit "t" does that automatically target the nearest healer or just the most powerful in the mob? It seems like sometimes when I use it, I will run about a mile away, leaving my teammates in the lurch. Which doesn't really matter because I usually use henchies when doing quests rather than my guildmates because they have all been through this stuff before and I want to experience things without help the first time around. Still though.

Also I use favorable winds a lot. the skill where you summon a spirit and your arrows hit harder. Does anyone know how far the effect of that spirit is? Does it affect all around the radar area or do you have to stay right next to it? It seems like if I wander to far there is no effect to it, but it could just be me.

I thank everyone in advance for your replies.

Favorable winds affects 3/4 the map area where its casted

Pressing T attacks the called target if of course your settings are still on default, i believe C is the closest target

If you look at the conditoins bar you can see when fave winds has either expired as it won't be there or if your out of range as it won't be there.

When you are targetting an opponent, look just under their health bar that has appeared at the top of your screen. The skill they are using appears just beneath it.