Max res. A must have for survival later on in this game.
You can increase your resistance in two ways. Through gear or by spending passive skill points towards it. Now, going for elemental resistance through your passive skills is only for build specific reasons (e.g. Righteous Fire builds).
The easiest way to max your resistance will be through your gear. Except for unique items, your gear will have random rolled mods so much of your resistance will be coming from randomly rolled mods on items that have synergy with your playstyle. However, "resistance rings" provide some resistance as a base mod and with a lucky roll also have extra resistance as some of their mods.
Ruby rings: Fire resistance
Sapphire rings: Cold resistance
Topaz rings: Lightning resistance
Two-stone rings: A combination of two resistances but a lower amount than ruby, sapphire, topaz rings.