At first, you'll just put all mid-grade equipment as a priority over all low-grade equipment. Doesn't matter much which ones you use, because you probably have other things you need to use your gold on. Then when you build up a big enough supply of mid-grade equips you can start prioritizing within them.

The items, in order of power addition, are: ring, bracelet, earrings, necklace. The gaps between each type are big, so it's seldom appropriate to deviate unless you want to bulk up all attack or all defense for some reason.

Personally, the only worn equips I ever upgrade are +10s. Eventually all of the ones you use will be +10 so you don't want to waste gold and XP in lesser equips for what is really a marginal gain early on. I do 'bank' XP in lower equips to save space by upgrading them once with one equip of the same type to get them to lvl 8-11. This also lets me upgrade a new +10 to lvl 30 in one shot and at a much lower total gold cost than half-stepping it with lvl 1 equips. Gold will become less scarce as you play, but the equipment inventory space is still a huge reason to keep on doing this.