The easiest way to tell if your pokemon card is rare is to look in the bottom-left corner of the card where you will see some icons. You will see two numbers separated by a /. Look to the immediate right of those numbers and you will see a shape of some sort. The shape will either be a circle, a diamond, a star, or a larger star with "Promo" across it.
Note: It may be difficult to locate the shape if you are examining a card with a shiny margin, such as GX, Vmax, etc.
Circle:
If you find a circle on your card, it basically means nothing special. Everyone who has opened a pack from this series most likely have this card. If you are lucky, you will find the evolved form of this Pokemon in the same series.
Diamond:
If your card has a diamond on it, you have found a card that is still easy to find, but is rare if you compare it to circle cards. Diamond cards usually have HP around 90-130 or so and have stronger moves. They are nothing to show off, but are great additions to your team if you play the card game. Diamonds are usually the evolved form of some other Pokemon.
Star:
If you found a star on your card, it has really strong attacks and high HP. It could also mean that your card is a EX, GX, Vmax, etc. If you are lucky, a star may just indicate a rare card, such as a shiny, which I will discuss later. Star cards are not expensive but are rare.
"Promo" Star:
If you found a "Promo" star on your card, that mean it was a featured/guaranteed card (that basically means it was displayed at the front of the box you opened) So technically, if you have a "Promo" star, it's not rare, but it's being featured probably means it's a really strong card!
Note: Some cards like first editions and foil/foil margin cards will not have a shape icon. "Ultra rare" and "secret rare" cards also do not have the shapes.
First Editions:
First editions are super rare and expensive. You cannot find them in your everyday packs that are sitting on the Walmart shelf, though. Usually they would be on display or for sale at a collectibles or trading card convention, if you ever get a chance to go to one. They are indicated by the illustrator, Ken Sugimori (the creator of Pokemon) and a queer background design compared to your other cards. If you think you have a first edition, look a picture of one up and make sure!
Shinies:
Shinies can be indicated by sparkles in the background and colors on the Pokemon that are different than they usually are. Shinies are very rare, but the money you can get with them varies widely depending on the stats, the rarity (GX, Vmax, etc.), and many other things. The shiny Swanna I have is about $2.00.
I hope this helped!
