I recently started up again, here's my formula:

Don't be cheap with your belt, get it big, and with fhr or res or both. Fill it with 1 slot of health, and load it with mana potions. Pick it up, and drop it, then fill it again. Keeping a surplus of mana potions will make the drain seem less painful.

Stack resists.

Ral+Ort in a helm, 2 or 3 os shield. Get a stealth or better armor (frw with res even better if you can get fhr as well)

Do about 10-30 Countess runs. Get all the runes you need. Fuse up your extras. Save your chipped/flawed gems.

Sell any high value items; wands, staves, sorc orbs, necro heads, druid helmets, etc. Then go play with Gheed or your favorite vendor a bit for some decent boots/gloves. Decent meaning, +fire or lightning res, and run/walk on the boots if you can. If you're getting 2 shotted, consider what source of damage is two shotting you. If you're wearing quilted armor and leather gloves in A4, you're probably having a bad time.

Murder some ancients, then run Baal if you're playing online. A 4 os or white long or crystal sword should drop during your runs. Use your socket quest on it if you have to, and make a spirit. The +skills will go a long way for your passives. Speaking of which -

Drop just one point into Warmth, Energy Shield, Frozen armor, and later in your career around level 40 or so, you can comfortably drop one into Shiver Armor

That last tip is regardless of your build.

Don't skimp on doing Izual, Radament, Save the Barbs, and Anya. The resistance buff feels like cheating if you're coming from classic. Also, don't worry about "wasting" your imbue. I still know people who are "saving it for something good"... and 15 years later, here we are.

Then hit Nightmare, build that insight if you haven't already.

You'll still be mostly potion reliant when teleporting, but the regen will cover your casting for the most part.