Hatsukoi mada nai

I have learned piano for only 1 year. My teacher does'nt teach me anything about composing skill T.T So i learned myseft and this is my first song. I know it too short and not good at all but I still would like those professionals to give me some suggestion to improve my composing skills, thanks you :))

Hatsukoi mada nai.mid

Engraving through this entire thing is super awkward and cluttered. Dynamics need to be marked without interfering with other markings, trills and octave notation can't be so close. Spacing makes something look professional. 

m. 14 - Never assume that the accidental carries throughout the octave. Sharps belong on both notes of the octave.
m. 22 - I'm not sure why you would put this here, since it's the same register as the next note in the soprano. If you meant an octave down, just mark it on octave down. 
m. 26-29 - Weird way to write this. Simply use the 8va and stretch it all the way towards the end.

Overall: A lot of non harmonic tones that should be dealt with... things that can't be explained away using pedal tones. This is mainly a problem later... mainly with your 5 chords that hold a minor sixth in them, when that's the thing that should be resolving.

I don't think there are objective things to say about the piece. You are in the beginning of the composer's journey, and the naivity is clear throughout the piece. Time will make you grow more mature, and it will be implicit in your future compositions.

If you don't have any training or study in composition, I recommend you start with a good harmony book (like Hindemith's or Schoenberg's, although this last one is less practial sometimes and more philosophical... there are many harmony books out there). It will at least open your eyes for some chords other than the small amount you use here.

Listen to as many pieces as you can. If possible, listen to it with the score and try to understand more or less what they did there. As you're studying piano and composing for it, you could look for some composers that have made good works for piano. Well, could I list some? Bach (not exactly piano, but ok), Mozart, Beethoven, Brahms, Chopin, Schubert, Liszt, Ravel, Debussy are quite standard. Look for the style you like and pursue it until you realize that you're done with it and want something new (happens to everybody, been there, bro).

So... 初恋まだない？かわいそう...でも、来たらもっと大変だと思うよ。

It is early in your composing career, but keep practicing! Just remember that practice is the mother of skill. Every piece you write, you improve. I like the advice above. Have some intense listening sessions of composers you admire, and study the chords they use. Try copying an aspect of a piece. For example, take a Chopin waltz and write out all the chords he uses, then try to compose your own melody over that chord progression. Start with a melody that only uses chord tones, then add in some passing tones between the chord tones. There is nothing wrong with copying as an educational exercise, and it might open your eyes to a whole new batch of chords you've never experimented with before. Try different rhythms and textures. Think of this as a "laboratory" where you can experiment in any way you like.