For verification of Ohm's law we use a battery source, an ammeter, a voltmeter, a potentiometer, a long wire made of some substance like copper. We may use a digital multimeter for measuring current or voltage.
1. We must follow the instructions carefully during the experiment.
2. Do not connect (or place) the multimeter (leads/pins at the end of wires) directly to the ends of battery, when it is in current mode. It can damage the meter.
3. We must estimate approximately the range for resistances being used. We must have the appropriate ranges for the voltage and/or current sources. We should not choose a resistor of low resistance, because too high current may damage equipment. It may even burn the resistor wire or your hands.
4. Connect the wires neatly and tightly. Loose connections can give wrong readings.
5. Switch on the battery when reading current and voltage. As soon as they are done, switch off. That saves power as well as it stops the resistor from over heating. Allow for the resistor to cool down to room temperature before taking the next reading.
6. Check the temperature of the resistor to be at room temperature at the time of reading meters. Resistance increases with temperature. It is useful to immerse most of the resistor in water while doing the experiment. Water will maintain the same temperature. Measure the temperature also. So that it can be reported along with other results.
7. Take a number of readings for different lengths of the wire or different samples of the resistor of different shapes and weight.