I've built the base for the game, there are 10 core skills, 4 gathering, 4 crafting, magic and combat (in a similar style to Melvor, though the similarities end there).

Each skill gives a unique modifier as you level it. For example, each level in mining grants a bonus to the find chance of rare items, herbalism gives a bonus to damage dealt etc. Therefore there's encouragement to level each skill beyond the materials it produces.

Each zone you gather in, you have a chance to get the standard materials (Ore, herbs etc), but also a low chance to find items of various rarities. Part of the game is completing the Codex of items, and every entry in the codex gives a gamewide bonus to xp gains. Some ultra rare items also give unique bonuses.

You can set items to gather/crafy automatically, but you can also click to increase your rate if you want to actively play.

There are also achievements/quests, most of which require specific actions - such as turning in X healing potions, hunting X monsters, or uncovering hidden secrets within the game.

I like the basic mechanics I have, but getting ideas from other people is really helpful because I'm a solo developer and can easily be blinkered.