Picking out melodies in first position is a great place to start learning, it will teach you how to feel your way around the harp and where the notes are, also it’s something you can do straight away without any of the more advanced techniques.
I’ve tabbed out a couple of examples here but it’s up to you to try to play as many melodies as you can think of. You can start to learn with harmonica tab but I would advise against being too reliant on it, the aim should be to hear a melody in your head then be able to play it on your harp, like talking. Just keep in mind that when you’re playing that improvised blues solo, there won’t be no tab then!
Oh When The Saints