This chart might be helpful when picking out the right interval for your melody. The best way to fully understand and feel the effects of the different intervals, is to sit down by an instrument like the piano and just play around with them. Play a minor second (C, then C#), and listen to how it feels. Then play a C and G, and feel how a major fifth feels in comparison.
You can see from the chart that some intervals are associated with happiness, some with sadness and others with longing and strength. Use this to find the right character and interval for your melody, setting the mood immediately for the listener. If you look at the perfect fifth for example, it’s considered very heroic and powerful, making it a great fit for the Star Wars theme.
Try to use intervals to spice up your melodies, make them more memorable, and set the mood and emotion in a very clear and direct way. Trying out different intervals to begin creating melodies can also be a good way to find inspiration whenever you have a hard time coming up with memorable themes. Use the chart as a reference and play around with them – see where it takes you!