The Puzzler's Guide/Intro/General Strategies
First off, DON'T PANIC! The main thing to remember is that puzzles, no matter how hard they profess to be, want to be solved. As such, what you may think of as "impossible" on first sight may contain many more clues, hints and possibly useful bits of information which will all make solving the puzzle a whole lot easier. (Of course, you might still need to do some hard work, but we can't just sit around thinking all day now, can we?)
The first thing to do then is to work out what the puzzle wants you to do. With easy puzzles, this is usually spelled out rather obviously. e.g. "What comes next?", "Who dunnit?" etc. If there's no obvious puzzle to begin with, then you already know one thing you're looking for - a question. This is important - interpreting "random" information is a lot (or bit) easier if you know what kind of thing you're looking for - whether it's a word, a sentence, or even a picture or a reference to something else. Look for the question mark, it is usually a good signifier of what kind of thing you are looking for.
In terms of Perplex City Puzzle Cards, try entering your code and find out what kind of answer the puzzle setter is looking for. It will usually be a word or a number, but sometimes it might be a second name or a series of answers. The input form is as much a clue as the card itself.
So if you're lucky and you have a question, a good next step is actually not a step at all. It is an anti-step. This unstep is: don't jump to assumptions, at least not too quickly. It's easy, oh so easy, to start working on a puzzle after reading the question too quickly, and then realising - once you've used up your 3 daily guesses - that it actually wanted THIS, not THAT. Take your time, read the question. Make sure you know what you're looking for.
Always remember, Google is your friend. Puzzles which involve a bunch of words, pictures or numbers that seem unconnected might all come together if you simply perform a google search with them.
Tips!
1. What do you see? Look at every part of the puzzle, though some have red herrings, chances are you'll need to use every part of the puzzle to solve it, or the extra parts will at least provide a clue to help you.
2. Are there any recognisable patterns? Do you see a number or a colour sequence that looks familiar? are there any unusual symbols or characters that might help you? A lot of puzzles involve recognising patterns and continuing them or using the pattern on something else, try to find the significance of the pattern or sequence.
3. Find the easiest route. Once you've discovered what the puzzle is asking you to do, try thinking about the easiest or quickest way to solve it. Try to look up similar puzzles via a search engine like Google and find out if there are techniques that make that type of puzzle easier to solve.