One of the most common ways of creating tension when soloing is through the use of altered chords. The flattening or raising of 3rds and 7ths is common in basic chord construction, but the other degrees of a chord may also be raised or lowered. The most common altered chords involve alterations to the 5th and/or the 9th. Usually the alteration appears in the name of the chord. Here are some examples.
Although alterations can be made to any chord, the most common altered chords are dominants, e.g. the V7 in a II V I progression. Here is an example using a 7#5 chord (also called an augmented 7th e.g. Eb+7). Listen to how the raised 5th adds a different flavor to the line.