Gem Farming

I'm saving up gems by skipping the gacha banners because I really want to pull for Mitia, and I've finally managed to gather enough for 50 pulls! Farming gems itself can be quite rewarding if you're persistent, but honestly, it's a bit of a struggle for me... The amount of free gems given out feels small, and gathering the materials needed for character ascension is also tough. Well, this is entirely my fault, but I lack planning, so as soon as I save up gems, I tend to spend them all immediately. Plus, I'm pretty bad at the game, so I can't seem to gather enough gems or materials. I'm trying to get ready to welcome Mitia while I have the chance, so I've been diving back into Genshin Impact after a long time. I'd also like to gather the ascension materials beforehand if possible, but do you only find out what materials are needed when they're released?