Here's a common question: How smart are pokemon? Well, as you might have guessed it depends on the pokemon, but there are a few general guidelines that are good to follow.
Essentially, the best way to think of pokemon are as very young children. Many pokemon, especially the smaller ones like the birds, bugs, and Rattata/Nidorans, would operate more on instinct and repetitive training than actual logic. They wouldn't be able to communicate complex ideas, but only simple feelings and needs. Memories would be shadows, hard to recall. The only thing that is real for these type of pokemon is what they can see or feel in the present. They still have feelings and free will, of course.
Quite a few pokemon, typically the middle-level ones like Charmander or Seel, will have the intelligence of perhaps a one- or two-year-old. They will realize that when a trainer hides, they aren't really gone, and they might even be able to remember specific past events. Still, their sentences would be simple at best.
Only the smarter pokemon might be able to think on a five or six-year-old's level, with the ability to question the world around them. They'll remember things that happened, and not only 'memorize' things but 'learn' to understand them. The pokemon that form colonies, like Clefairy, would often be around this level. As pokemon this smart grow older and learn more, it's not unheard of them to develop even further, but it's *rare.*
The only pokemon that really think on the average adult human's level are ones that are highly evolved and experienced (like Dragonites, and psychic-types like Alakazam and Hypno) and naturally intelligent ones such as Lapras. It would be very rare indeed to see a Bulbasaur or Nidoran to be holding a normal, intelligent conversation with its trainer. (Sure, there might be special cases like Meowth, but in general pokemon just aren't that smart.)
Pokemon aren't so stupid that they're just fuzzy guns, popping out of their Pokeballs only to beat on other pokemon and then returning to their 'balls. Yet they aren't so smart that they're just furry humans with special attacks.
Most people we've seen are doing a good job RPing pokemon as-is, we just wanted to clear up questions and remind people that pokemon are only a few steps up from animals, and a few steps down from humans. Not every pokemon will say "<Wow, this Poke Chow isamazingly tangy!>" Some will only say "<Food! Good!>".