To clarify: Are you playing the expansion, or classic Diablo II? It makes a huge difference. For instance, in classic, you simply can’t rely on your hireling, since they die at the drop of a hat, can’t be resurrected, can’t be equipped, and (I think) you can’t take them with you from one act to another.
Also, are you planning on playing through all three difficulty levels, or just through normal? If just normal, you’ve got a lot of leeway in your build, but if you’re planning on soloing Hell, you’ll absolutely need at least something in each element.
Assuming you’re playing Classic (since you’re worried about Diablo rather than Baal) and that you’re planning on all three difficulties (since just Normal is easy): I would recommend Fireball, Frozen Orb, and Static Field. Static Field won’t kill anything, but in Classic, it’ll get anything (that isn’t lightning immune) very close to dead. Fireball will be your main damage spell for small groups of enemies or bosses, and Frozen Orb will be your main killer for those swarms of little things. Frozen Orb is also effective against single monsters, if you stand just the right distance away: The orb will explode right on top of your target, hitting it with half or more of the shards. You will occasionally (in Hell) encounter a monster that’s immune to both cold and fire; usually, you’ll want to just avoid these monsters. If you absolutely can’t avoid them (the Council in act 3, for instance), then you’ll use Static Field to sliver it (get its life down to one pixel), then finish it off with any other lightning skill (even Charged Bolt, if that’s all you have).
For stat points, you’ll probably want 75 strength (for a tower shield), just enough energy that you’re not continually guzzling potions, and all the rest in vitality. Energy shield can be nice, but unless you have a ton of points to spend on it and Telekinesis (its synergy skill… You are playing 1.10 or 1.11, right?), it’s no substitute for life. And with three skill trees to develop, you won’t have any points available to waste on Energy Shield.
On equipment, your ideal is Angelic Garb light plate or Twitchthroe studded leather for armor, the Spectral Shard dagger for a weapon, and either a socketed tower shield with three perfect diamonds, or Sigon’s Guard. Your amulet should have plus to sorceress skills, and your rings should have faster cast rate (ideally, they should be Stones of Jordan, but that’s not going to happen). The ideal helmet is probably socketed with three perfect skulls. Playing single-player, you might well not get all of these items; your next best choice for a weapon is a wand with +mana and/or faster cast rate (you can buy these from vendors), and for an armor, resists and life are more important than defense.
Finally, I might ask why you’re playing single player. If you have the expansion, you’re welcome to join other Dopers online, where we’ll be glad to give you a lot of help of all kinds. And playing with Dopers, you wouldn’t have to put up with any of the dweebs one usually finds in online games. We play on the realm US West, and can typically be found in a game called sdmb (or sdmb2 or sdmb3 or…) with password “cecil”.