Warm up before practicing advanced techniques. There are dozens of warm-ups singers do, but saying "Ssss" or "Shhh" loudly, "croaking" your voice, gliding from lowest comfortable notes to highest comfortable notes and singing scales are a few of the most common and successful techniques.
Maintain proper posture and breathing once you begin practicing the runs. Avoid slouching, even when not singing, and do not hold your breath to fit more notes into any sung phrase. Remember to breathe outward instead of upward.
Know the specific notes of the run you wish to sing. Many people think that you can just pick any random notes to sing in a run. However, as with guitar playing, most improvisational runs come from different arrangements of the musician's memorized reserve of note patterns.
Split the run into small sections, or riffs, which are usually two to five note patterns. Practice the melody of each section until you are confident in singing it.
Begin to slowly sing the notes a cappella, combining the riffs to make your run. Use a metronome if you wish to practice timing. It will more like a simple melody for a song than a run.
Speed up your singing gradually, and add musical accompaniment.
Practice singing the run with different vowel sounds, such as "ee," "oo" and "oh." If you are singing a specific run that is a part of a song, practice changing the sound of the run as it does in the recording. If your run is the vowel of a certain word, such as "me," practice transitioning to a similar vowel. Because "me" should be pronounced more closely to "may" when sung, a smooth transition vowel to sing is the short "a." In this example, it would sound as if "me" changed to the word "yeah."
Sing in real time with musical accompaniment to practice singing your run quickly and at the appropriate time. Listen for musical cues and certain notes that can guide you when to start runs.
Listen to songs by professional singers. Learn their songs, study how they form runs and riffs, and imitate their performances.