A sequence is a melodic idea that's repeated up or down by step.

Take your melody from bar 1 and repeat it up or down a step in bar 2. Repeat the process again for bar 3. End the sequence in bar 4 with a long note, or with rests to give the melody a sense of breath.

Tip: Try using chord tones (notes of the chord) in each bar, especially on the 1st beat. For more on this, go to Outlining.