The most common scale used in blues guitar playing is the minor pentatonic scale. Pentatonic means five tones, so in practical terms this means that once you have played five different notes the scale repeats itself an octave higher than you started. Here is the minor pentatonic scale in the key of A.
Play the scale as indicated here. It should sound familiar to you. The symbol t is used to down stroke of the pick.
Now try starting at the highest note and playing down through the scale.
Now play the scale ascending and descending as shown here. Try to get a smooth, even sound. The symbol y is used to indicate an up stroke of the pick.
To help develop your picking it is a good idea to practice playing each note twice, alternating down and up strokes.
Playing three times on each note is a very good way to develop alternate picking because each new note starts with an opposite stroke to the last one.