A lot of people have trouble with skills, mostly with the 'meager' amount of 8 slots to pick from. I've now played with all professions as primary and I can say that the 8 slots are enough, really. For PvE anyway.
A mistake commonly made is to stack up all 8 slots with attack skills. Not smart. In PvE you're usually walking around with people whose skills / abilities you don't always know. It might be smart not to (over)specialize in one direction.

I've had a lot of success with this basic formula for skill distribution:
Blinding Dervish
Dervish/Warrior
Ebon Dust Aura
Scythe Mastery 16 (12+4)
Earth Prayers 10 (9+1)
Mysticism 9
Ebon Dust Aura
Vital Boon
Mystic Vigor
Pious Haste
Crippling Sweep
Victorious Sweep/attack skill of choice
Chilling Victory
Resurrection Signet
Equipment needed:
Ebon scythe. To make an ebon scythe, unlock an Ebon Scythe Snathe from the Priest of Balthazar for 1,000 faction, or unlock one in PvE. Ebon Dust Aura will not work without an ebon scythe.
Concept:
Melee shutdown, repeated Blindness and Crippling, survival.

Slot 1-4: Attack skills
I generally go for a signet or such in slot 1. a 5 energy in slot 2 and 10, 15 in the last 2 slots. In case of a warrior, never take more than two adrenaline based attacks. You'll just make yourself to dependent on Adrenaline and you'll have to fight the urge to rush.

Slots 5-7: Helaing & Defense skills
Whether you should do this in a "2 Healing, 1 Defense" or "1 Healing, 2 Defense" configuration is largely dependent on the available skills and what you expect to find in the comming Mission/Quest. If for example you'll meet lots of Disrupting Critters (Devourers eg.) go with an extra Defense that'll let you do your thing uninterupted. Make sure you can cast your healing skill(s) on yourself as well :-)

Slot 8: Ressurrect Signet.
Hammer this one into place. Only replace it with a spell that has the same effect, i.e. a living partymember who was dead before using this skill-slot.

Specialization
The above formula let's you create a well rounded character that can deal damage, heal himself/others a bit if needed and can res partymembers in battle so the monk doesn't have to stop healing.
Now, if you explictly want to specialize, do so only if running with people you know (Guilds or friends) and make sure people know about the specialization.
I'd still recommend not using more than 5 skills, 6 at the outmost on a specialized build. Leave one heal and one res available.

Utility Skills (Mainly Rangers)
What I do is sacrifice one or two Attack and one Healing skill to Utility skills such as Traps, Pet and Spirits.