For example, if you install a 2N4304 transistor in the hole for the 2N4306, you'll catch your mistake when you get ready to install the 2N4306 and can't find it. If you use this technique, you will be populating the printed circuit board with a lot of parts at once. One technique to hold the parts in place as you turn the board over to work is to bend the leads out at a 45-degree angle. Some parts have a precise polarity in which they must be installed, while other parts can be installed either way. Resistors, toroids, coils, chokes, crystals, ceramic disk capacitors, and monolithic capacitors can not be put in the wrong way.
Electrolytic capacitors have a positive and a negative side.
Trimmer capacitors will work in either orientation. So be sure to match the flat side of the trimmer capacitor with the silk screen diagram to take advantage of this orientation. When you put in the I.C.'s, be certain to match up the dot on the I.C. with the dot on the layout diagram. You may also notice that each of the sockets has a notch. Align the notch so that it is oriented with the dots.