How to tell if a Pokémon card is rare

Look at the bottom corner of the card for a small symbol next to the collector number. A circle means common, a diamond means uncommon, and a star means rare. Everything beyond that, including secret rares and full-art cards, is signalled by a collector number higher than the set total or by artwork that runs to the card's edges.
- Find the rarity symbol. Look at the bottom of the card near the collector number for a circle, diamond or star.
- Compare the collector number to the set total. If the card number is higher than the set total, such as 115/114, it is a secret rare.
- Check the finish. Tilt the card under light to see whether the artwork is holo, the border is reverse holo, or neither.
- Confirm the set. Match the set symbol to the correct release, since reprints of the same artwork carry very different values.
The rarity symbols, in order
Three symbols cover most cards you will pull from a pack. A filled circle is common, a diamond is uncommon, and a black star is rare. The symbol sits beside the collector number in the bottom corner, and it describes how often the card appeared in packs rather than what it is worth.
Above those sit the modern rarities: ex and V cards, full arts where the illustration covers the whole card, and secret rares numbered past the end of the set. These appear far less often, which is where real scarcity begins.
Rare and valuable are different things
A rare card from a heavily printed modern set can sell for less than an uncommon from 1999. Print run size, how many copies survived in good condition, and whether the Pokémon is popular all matter more than the symbol stamped on the card.
Charizard is the clearest example. Almost any Charizard carries a premium over a card of identical rarity featuring a less famous Pokémon, purely because more people want it.
Watch for first edition and shadowless prints
First edition cards carry a small stamp showing a 1 with EDITION curved above it, and they only exist in ten early English sets, from Base Set through Neo Destiny. A card outside those sets claiming first edition status is not genuine.
Shadowless Base Set cards are subtler. They lack the drop shadow to the right of the artwork frame that later printings have. Collectors pay a significant premium for them, and the difference is easy to miss unless you compare two cards side by side.
Questions
Does a holo card always beat a non-holo?
Usually within the same set and card number, yes. Across sets it breaks down quickly, since a non-holo from a scarce early set can outprice a holo from a recent one.
What does a collector number like 115/114 mean?
It marks a secret rare. The set officially contains 114 cards, and this one sits beyond that count, printed in smaller numbers than the rest.