Whether you like music theory or not: Scales are one of the cornerstones of songwriting in nearly any genre. It doesn't matter if you produce EDM, rock, urban beats, pop, or any other style. Knowing the basic principles behind the different scales will make your songwriting soooo much better.
Basically, scales are just a collection of notes that "sound good together" and that you can use to create a certain atmosphere in your song. Instead of juggling around with all twelve notes of the octave you just concentrate on a few of them. This makes it way easier to find nice melodies.
The two most important scales of Western music are called the Major and the Minor scale. The Major scale is mostly used for happy, upbeat songs. The Minor scale is more interesting for thoughtful, sad, serious songs. More than 80% of modern electronic tracks use the Minor scale.
As I said, a scale is a collection of notes. But each collection has one note that is especially important. This note is called the root note of the scale. And it is always the first note that is listed when you talk about the notes of that scale.
Starting from the root, each scale has a special mathematical recipe how you construct the rest of the notes. For example, the Major scale is constructed like this:
1st note = Root note
2nd = Root note + 2 halftones
3rd = 2nd + 2 halftones
4th = 3rd + 1 halftone
5th = 4th + 2 halftones
6th = 5th + 2 halftones
7th = 6th + 2 halftones
Let's take a look at C Major. It consists of all the white notes of the keyboard, and the C is the root note (hence the name). When you start from the C, you can calculate the second note by adding two halftones. One halftone is C#, two halftones is D. Use the construction rules from above and you will see that you end up with the white notes.
If you play the notes in succession, you will notice that they create a special feeling. This feeling is created by the intervals between the notes. Most people are so used to the special intervals of the Major (or Minor) scale, that they can immediately recognize it and hum along.
As you can see, you can use the construction formula from above to create any Major scale. E Major for example will result in E, F#, G#, A, B, C#, D#. Play the notes in succession and they will create the same feeling as C Major - just a few notes higher.
Unfortunately the notes of E Major are not as easy to remember as the notes of C Major, so many people tend to use C Major way more often. But there are good reasons to use other root notes as well. Here are some of them:
Let's take a look at A Minor:
Surprise! The A Minor scale consists of the white keys as well. So, do the C Major scale and the A Minor scale sound the same? Nope, not at all!
The two scales are definitely related to each other, but due to the different root notes they sound differently. The order of the intervals is the important point. When you start to play on the A and then move up, you work with different intervals than when you start from the C.
And this is essential for your songwriting: You really need to put focus on the root note to make it clear for your listeners on which scale you work and what they can expect from the rest of your melodies. Otherwise your song will feel a little bit confusing. Starting your melodies on the root note is a good way to do that (you don't have to, of course). And it's also a good idea to get back to the root from time to time.
If you know the notes of the Major and the Minor scale, you also know where you can take your chords from. Basically you only work with chords where all the notes lie on your chosen scale. Software like Sundog makes it easy to work with the most important chords of any scale instantly. You may also want to take a look at the Scale Chords project for some inspiration.
There are two other scales that are very popular for writing melodies. The first is the Major Pentatonic scale, the second is the Minor Pentatonic scale. They both consist of five notes. These notes are a subset of the "full" Major or Minor scale respectively.
C Major Pentatonic = C, D, E, G, A
A Minor Pentatonic = A, C, D, E, G
So, why are these two scales so interesting for melodies? They both consist of only those notes that sound good together. If you play all the notes of C Major at once, it sounds quite harsh. But if you play the notes of C Major Pentatonic, it's absolutely OK.
This is because the intervals between the single notes are big enough that the notes don't interfere with each other. If you go from one note just one halftone up, the two notes are so close to each other that they sound dissonant together. C Major contains such a problematic step when you go from E to F. As you can see, the F is not included in the C Major Pentatonic scale. This is why you can jam around safely on the pentatonic variants.
This is just a basic guide, so we will stop here. But there are plenty of other scales, and some of them are really popular in different genres (especially in world music). For the start, you may want to take a look at the Western modes, which are related to the Major and the Minor scale. Many other scales are listed at the free Scale Chords project.