finish some quests and upgrade your farm (mining) using pokke points. you can usually mine those jewels at mining spots anywhere on your current map. it's also rewarded to you after clearing some quests. if you really want more mining spots, go for the volcano quests. bring old pickaxes and the normal ones. dont forget to bring cold drinks. inspect every wall that has a crack and equip your pickaxe. if the pickaxe is highlighted on the wall, then go ahead and mine like crazy.
at the start, you can be overwhelmed by the sheer amount of items you may get but you'll get used to it. just refer to the monster hunter wiki for more info.