General Tips for Laboratory:
The laboratory is not a contest whose object is to get the "right answer." The purpose is to learn how to gain knowledge by looking at reality, not an attempt to make reality conform to preconceptions. The important thing is to learn how to be observant, to really see what happens, and to deal with this information with the strictest integrity. And to understand, or learn to understand, the meaning of what happens.
Even if you get results totally at variance with theory (as may happen due to a mistake, or a systematic uncertainty) you will get a high grade if you report it honestly and demonstrate that you understand what you did and how your results occurred. (If you have trouble interpreting your results, contact your TA for help.) On the other hand, if you get perfect agreement with theory by faking your data you will fail.
Practical ability to do experiments and analyze data is usually acquired through practice and experience. Practice is very important in learning any new discipline. A good lecture may be very helpful but not fully useful without actual practice. In experimental science, practice involves solving many problems (i.e. homework) and performing a variety of experiments (i.e. labs). Practice is essential to being able to make the connection between theory and experience.
Laboratory is a place that is equipped and prepared for the following purposes: