For tests, memorize the values in whatever text is being used. All facilities have different ranges for what they believe is normal. If it is for a test, remember, that most of the time, lab values will be presented to you as a "critical" value; either really high or really low. But also remember that the parameters are the parameters. Don't let your mind sway you into choosing the wrong answer. for example, electrolyte protocols will have exact values to follow. If the parameter value for a certain lab is 5-20 *no change, and you get a lab result of 20, DONT CHANGE IT. It is kind of like the sliding scale with insulin administration, if that helps you understand.
In memorizing these values, know what range you are expected to know. Sometimes simply asking the instructor what ranges they will be using is a quick and easy way to save you time and stress. Once you know this, do what previous posters have recommended and make flash cards. Go over these until you know them for a test, and find out little ways to remember them (this will usually come up when you are reviewing them with another student) and for example the way I remembered BUN was to think about it as the pant size for women; and your "buns" go in pants so your BUN(s) go in 8-20 size pants.
Regardless, repetition of lab values is the best way to remember them. Do this throughout nursing school, being tested or not, and it will help you in the real world.
Good luck to you!