Prepare both perfect and imperfect cadences with a predominant chord. The most typical predominant chords are IV and II. Typically the II chord is used in first inversion, meaning that the fourth scale degree is in the bass.
Form the first half of a perfect cadence by moving from the predominant chord to the dominant. In general, the bass will step up from the fourth scale degree to the fifth, and the inner two voices will move downwards against it. The top voice might move up or down, depending on the melodic motion. Remember to raise the leading tone if your progression is in a minor key.
Complete a perfect cadence by moving from the V chord to a I chord. The bass should either move down a fifth or up a fourth. If in the V chord the root of the chord was doubled, maintain the common tone from the V chord to the I chord. The movement of the upper voice is primarily determined by the melody. In general, the middle two voices will move against the direction of the bass.
Form the first half of an imperfect cadence by moving from the predominant chord to the tonic (I) chord. The bass can either move down by step to form a tonic chord in first inversion, or jump down a fourth or up a fifth to form a tonic chord in root position. Maintain the common tone (the first scale degree) between the two chords.
Complete an imperfect cadence by moving from the I chord to a V chord. The bass will either move up a fifth or down a fourth. If in the I chord the fifth of the chord was doubled, maintain the common tone from the I chord to the V chord. As in the perfect cadence, the movement of the upper voice is primarily determined by the melody, and the middle two voices will generally move against the direction of the bass.