I have a magblade. A couple of skills you might want for it are Path of Darkness and Strife. I morphed Strife to Swallow Soul, and it's the single most useful skill I have. I also use some skills from the Destruction Staff line like Wall of Elements.
I use Mother's Sorrow/Julianos on my Magblade with all 64 points in Magicka. all Magicka enchants on armour, recovery on jewellery add weapon damage on staves(Inferno both) I also have a Valkyn Scoria shoulder for the health boost. With Orzogas Frothgar, this gives me 17k health, 35k Magicka 9.5k Stam. Magicka regen is about 2.3k, so sustain is not a real problem. I agree with SyneyGrey that Swollow Soul is the most useful skill, and Merciless resolve should be early in your rotation to allow it time to build stacks; it needs 5 l/h attacks to get the Spectral Bow.
Magblades are super fun. They’re largely about pumping more into max magic and damage...look for sets that do this, and focus attributes on magic.
They will have excellent resource mgmt through leeching/siphoning strikes (always get which is which confused...the magic one, obviously). Merciless resolve is a core skill. It’s also one of the wonkier skills, and it can be hard to master. But work with it and learn it...it’s damage potential is massive when used well.
If you’re coming from another class, or are new, make sure to review the nightblade class passives carefully. Slotting different skills will create big differences. For example, having one siphoning skill slotted increases max magic by 8%, so always have one of these. Assassin skills boost your crit per skill slotted. And using a shadow skill offers a massive defensive buff through the passives.