Hi everyone! I'm kind of super ultra new to Sylestia- I literally joined a few minutes ago x-x
I would like some advice as to how to progress through the game. Not just the story part, but how to acquire good pets and avatar items. Also, what makes pets and avatar items "good" or "cool". And I also don't get the whole thing about themed pets. What are they? Like, are they just pets with certain color schemes? What's the best way to get gold? Can you get diamonds just by doing things in the game, or do you need to buy them?
Ok, yes, I have too many questions.
But I'd also like to just chat, if anyone's up for it.

Welcome to sylestia, to answer your questions:

1. you can catch (in the wild) or buy pets (from others players/merchan), the avatars items are mostly droped from festivals bosses or you can buy them with tokens in festivals. Outside of festivals you can look the trade broaker for items that could interess ou or make an anouncement in the item auction forum.

2. The value of a pet or item is generaly subjective however, max stat pets by exemple, are worth more as they take time and resources to get, a bit like the old retired avi items or the old monthly.

3. Themmed pets are a special type of pets that have a perticular color scheme and a tag, they can be tagged, witch mean that they are the first of their lineage, or PB (pure breed). Depending on the traits and themme they have different values.

4. You may nead to get mission pets to get as mutch gold as possible by sending them in mission, it is the quicker way to do it.

5. You can use the curencie exchange to trade gold for diamond, keep an eye on the advent calender, you may be able to get 100 diamonds from it at some point.

My number one recommendation is to avoid getting pets in the beginning. (Other than your 3 party pets, and possibly a few mission pets, of course.) Just focus on finishing the storyline. Once you get to a place where your gold earnings are sufficient, that is the time to collect pets, or start projects.

SOMTHING TO NOTE: if you EVER need help ask somebody like Krinadon they're a creator of this game and as such they know everything about it even the tips and tricks also to ping you press the blue @ button at the bottom of the post

well first off welcome! second seems like most of your questions have been answered above but any advice? hmm...think before you buy and take the time to familiarize yourself with the game and the community before you buy a ton of pets. Once you have a more grounded idea of how things works and a fair start of gold it's more fun and easier to keep up with the game. People are generally very friendly so don't be afraid to join in games/clubs or just talk to someone!

Also I absolutely LOVE your starter pets design!

Avatar items can be obtained in a couple ways.

The fastest way is to buy them from other players via the Broker. Of course you need gold for that so it's not very cost effective.

There are 5 main types of items that you'll find in your wardrobe: Explore, Forum, Seasonal/Fest, Diamond Shop, and Monthly Items. Explore items are obtained through actions in the world/storyline. Some are dropped by enemies, some have to be bought, and some have to be earned. Forum items are all prizes given out as forum game prizes. Most forum games happen during fests but there are exceptions. Fest items can only be obtained during their associated festival (aka fest). They may be dropped by fest bosses, bought from the fest store with fest currency, or found in a specific manner in fest events. Diamond Shop items can be bought anytime with diamonds from the diamond shop. Monthly items are an old type of item. There used to be a new set released monthly that players could buy with diamonds but they've since been discontinued. Nowadays you can only purchase them during the Black Friday sale.

About diamond, you either have to buy them with real money.

Or there is a currency exchange but better wait for that, since you have to exchange it for gold.

And there are the forum games where you can get some diamonds. I got my first diamonds ever like that. :)

Also, do you like sci-fi or fantasy?
And do you watch Hermitcraft? (if you don't know what it is just asked)

Yes! Sci-fi and fantasy are amazing. Wings of Fire was probably my favorite fantasy book series as a little kid. I still love it :3
I'm a huge book nerd, though I haven't seen many of those super popular sci-fi/fantasy movies. Not really a movie girl... Except for Fantastic Beasts.
What is Hermitcraft? I think I've heard of it before, but I'm not sure where.

It's a Minecraft series where a group of youtubers plays together. It's really fun. ;) Don't know why I didn't start earlier T^T

You should at least try season 6 before it's end ;)
Ps: We don't know when it will end. So some seasons are longers than others. :)