if you're going the melee way a few useful skills early on would be uppercut/puncture, flame whip, dark talons, cleave/flame breathe. general rule is equipping about 2 AOEs and 1 knockback/root + stun could greatly aid your survival against groups.

for 1H users try buffing up with razor and then alternating between searing strike (for the dot & heal) -> heavy attack -> flame whip -> heavy attack -> flame whip for single targets, complement with fire breathe for groups

for dk mages destructive clench is great for early survival, similar to uppercut in that it allows you to solo pretty much every boss except those immune to stun/knockbacks. fire ring is still one of the best aoes around to quickly clear groups of mobs

Might not be possible to learn all the skills, not sure if that will change in future updates

For now at max level (VR14), you may have enough to learn about 75% of all your skills & morphs.

Best would be to invest fully in your race abilities, 2 weapon skill trees, 1 armour skill tree and 2-3 crafting trees (enchant is pretty useful when you reach max).

You don't need to learn all the skills in a skill line, if you want to level up a spell just make sure it's in your action bar when you gain experience (killing enemies, pvp, unlocking chests, completing quests, dungeons etc). Skills that are not in your bar will not level up unless you read books.

When you reach max level in a skill, you can swap it from the action bar with a lower level skill when you turn in quests/open chests etc so that the experience gained will contribute to the lower level skill, instead of being wasted.

Armour & weapon skill lines will level up depending on the type of armour/weapon you equip in each slot, plus bonus for each amour/weapon-related spell you equip in your action bar.

Stealing and opening chests/safe boxes will level up Legerdemain.

Crafting skills will level up when you create/deconstruct/improve equipments.