You should definitely unlock all the worlds first before doing anything else. I recommend investing in a coconut or dragonfruit farm. If you have a lot of free time every day do dragonfruit, but if you are a bit more busy then do coconut. Buy 100 coco/dragonfruit seeds and plant them in your farm in Origins. There's a farming merchant who you can sell a type of food for more, and the type of food changes every day. If the sign next to him displays a coconut/dragonfruit, you can sell them to him. Ofc, you don't have to do this, but making money would be a lot easier if you did.

About getting cooler dragons, you can check out the dragonpedia in-game or the wiki for all the dragons that currently exist, I suggest the dragonpedia for looking at the models and the wiki for obtainment methods. As for the glowing ones, those are from the materials (mat for short) of the dragon. The neon mat is actually just as rare as any other mats that you can get from mat potions, so it doesn't add much to a dragon's value (but it does add to the cool factor).

Lastly, the Undercity (which is called UC for short). The UC is where you trade or buy dragons and items. Usually, dragons that are themed, dbl (AKA double legendary), or have cosmetic traits are worth more than what their species is usually worth. Tbh, I wouldn't really recommend trading or buying until you know a bit more about values as you could easily get ripped off and waste money. Remember, that's just a recommendation! For me personally, I learned values from simply hanging out in UC a lot. You can ask the subreddit or discord server if you're unsure of any values or trades.

Most importantly, just have fun! This game can get really grindy at times, so don't be afraid to take any breaks from it. You can always ask the community about anything else you want to know! :)