The more familiar you are with a scale, the easier you will find it to play melodies created from that scale, as well as creating your own melodies from the scale. One of the best ways to practice scales is the use of sequences. A sequence is a repetitive pattern in which the rhythm remains the same while the notes are repeated higher or lower, usually within a specific scale or key. Practicing sequences is also good for you co-ordination and picking technique. Remember to use alternate picking on all the eighth notes. Here are some sequences within the C major scale.
This sequence uses intervals of a 3rd. For more about intervals, see Progressive Jazz Lead Guitar Method or Progressive Complete Learn to Play Rhythm Guitar Manual.