Okay, here goes for me trying to teach melodic dictation...
You need time to build up your recognition of pitches. Regular practice is indeed important.
Start with REALLY easy cases. Like, for example, two notes, one after the other. In other words, learn to identify intervals well. Intervals are super important!
After a while, you can make up your own short string of notes, say, on your instrument or whatever, and try to identify more than one interval in quick succession. Note length/rhythm is not important for the most part - if you can keep track of which note corresponds to which pitch you're hearing that should suffice.
Here are some quick pointers to help you along the way though during your dictation:
- Listen to the last note if in complete doubt. It should be the tonic note in 99% of cases.
- Likewise, the first note is most likely the tonic too. If not, your next best bet is that it is the dominant. Is it the same pitch as the last note?
- Listen for scalewise motion. Does it sound like tone/semitone intervals? It's most likely one pitch up or down on the stave.
- This leaves the bane of melodic dictations which is the leap intervals. These usually will be 3rds, 4ths or 5ths. Again, there's no real shortcut here: just know where they are on the second listen through. You need that interval recognition practice!
That's all I can really give from off the top of my head - good luck.