Basic solo build tips:

1.) Decide if you want to be Magicka focused or Stamina focused.
- Invest in one stat or the other but not both, reason being your damage output is factored off of the stat that powers the ability. If you go 50/50 in Stamina and Magicka you're basically nerfing your own damage potential.

2.) Decide on your weapons and stick with them for a while.
- Hopping around to try out all the weapons a little is fine at first, but if you spew Skillpoints across multiple weapon skill trees (read: more than 2) you'll find you've spent points on skills you can't use (because you can only have 2 different weapon sets equipped at a time.

3.) All of the weapon types have something to recommend them. Here's some things to watch for:
- Resto Staff: Useful even if you're NOT a healer. Since you're solo, it can help a lot in reducing downtime and surviving encounters were the fights are a close call.

- Sword and Shield: The weapon set for Tanks. Still useful solo, but damage is low. Not a problem necessarily though as your Nightblade skills can be put into service for dealing damage. S&S also offers NB's a missile reflect option which they otherwise lack.

- Dual Wield: Currently has the best AoE in the game. Also lets you wield 2 weapons (obviously) which lets you get a deeper set bonus from crafted items (S&S does the same) and gives the best critical strike chance once you've unlocked all the passives.

- 2 Handed: Offers a damage shield (which is nice), a gap closer (which is unneeded), a knockback (for some control) and a damage buff (unneeded for NBs) and a self-heal. All around a lot of interesting tools.

- Bow: Best ranged damage dealing option. Pretty obvious why you'd want to use this one.

- Destruction Staff: For a Magicka NB, Destruction staff attacks (and Resto ones) will recharge your Magicka. (Ditto the other weapons and your Stamina). Destruction Staff also offers some control, and an AoE.

4.) Nightblade skills to get/look forward to:
- All of the Ultimates are good. Get them all and build each up so that you can morph it.
- Assassin's Blade is your execute power. Get it and use it a lot to end fights faster.
- Teleport Strike is your gap closer and a stun. Highly useful for engaging when you can't get around behind the enemy.
- Mark Target is your enemy debuff and a massive heal. Get it when you can and mark everything (one at a time).
- Shadow Cloak is your condition cleanser and lets you sneak past impossible to avoid mobs in strategic bursts. Do NOT think of this as Stealth from other games. It's duration is incredibly short and is for use for surgical bits of invisibility only. Also mobs do not lose aggro on you when you Cloak.
- Veiled Strike is your highest single target damage ability, especially out of HIDE (aka crouching down).
- Aspect of Terror is highly useful in PvP, and somewhat useful in PvE as an AoE control that can buy you a few seconds of respite.
- For a Magicka NM, Strife does pretty decent damage and offers a nice self heal. It can be a solid part of your arsenal.
- Drain Power is your Major Damage buff. Get it and use it a lot once its available
- The Passives: Take all passives, everywhere pretty much, but prioritize ones that give you more resources (Stamina, Magicka or Health) or reduce the cost for your abilities.

Beyond that? Just get out there and quest. If you run into something ugly, ask a guild mate for help. If you don't have a guild, listen to shouts in the major cities and join one that sounds good.