Reducing error in the lab is important! There are three types of error to avoid:
Systematic error - be sure that all instruments used for measurement are in good condition, clean, and properly calibrated. For example, if using an electronic balance, be sure the readout is zero before placing an object on the balance pan.
Random error - be as careful as you can to reduce human impact on measurement. If you have a lab partner, come to an agreement on estimated parts of a measurement.
Gross error - be prepared for your lab work! Read directions ahead of time, keep your lab area clean and organized, and work as carefully as you can!