Except for the reading questions, each type of question on the SAT is arranged in order of difficulty. The first third of any type of question are easy, the next third are medium, and the last third are difficult. The progression is gradual so that within, say, the hard questions, the difficulty goes from easy-hard to medium-hard to hard-hard.
Is this always true? Yes. Sometimes you'll encounter a medium question among the easy ones, or a difficult question among the medium ones, but otherwise the increase in difficulty is something you can count on. You will never, however, encounter an easy question among the difficult ones.
An easy SAT question is one that most students get right. A hard question is one that most students get wrong. It's as simple as that.
It's important to realize that a hard question isn't necessarily difficult in the way that, say, calculus or organic chemistry is difficultbut it is always dangerous. For whatever reason, most students will get a hard question wrong.
How can you tell whether the questions are getting more difficult? The only sure clue is location: easy questions are in the first third; hard questions are in the final third. On the writing questions you'll have no other clues. At least on the sentence completion questions the vocabulary will become noticeably more difficult. Watch your step on the math questions. You'll notice the math problems generally becoming harder, but some of the most difficult questions often look simpler than the easiest questions.
In short, difficult questions do not always look difficult. Difficult questions that look easy are killer rabbits. We'll examine killer rabbits in depth later, particularly regarding the SAT Math Test.